Find, fix and prevent vulnerabilities in your code.

Overview

activesupport is a toolkit of support libraries and Ruby core extensions extracted from the Rails framework.

Affected versions of this package are vulnerable to Regular Expression Denial of Service (ReDoS) in number_to_delimited() in the NumberToDelimitedConverter. An attacker can cause excessive resource consumption by submitting excessively long digit strings.

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 activesupport to version 7.2.3.1, 8.0.4.1, 8.1.2.1 or higher.

References

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

Overview

Affected versions of this package are vulnerable to Infinite loop in the AtomicReference#update function when the current value is Float::NAN. An attacker can cause indefinite busy retry loops and CPU exhaustion by supplying malicious numeric data.

Remediation

Upgrade concurrent-ruby to version 1.3.7 or higher.

References

• GitHub Advisory
• GitHub Commit

Overview

rack is a minimal, modular and adaptable interface for developing web applications in Ruby. By wrapping HTTP requests and responses in the simplest way possible, it unifies and distills the API for web servers, web frameworks, and software in between (the so-called middleware) into a single method call.

Affected versions of this package are vulnerable to Exposure of Information Through Directory Listing in Rack::Directory, which checks for presence in the root directory only by left-side string comparison. An attacker can list directories outside the intended root if the prefix of the target directory is exactly the name of the root directory. E.g. www_backup is exposed when www is intended.

Remediation

Upgrade rack to version 2.2.22, 3.1.20, 3.2.5 or higher.

References

• GitHub Commit

Overview

rack is a minimal, modular and adaptable interface for developing web applications in Ruby. By wrapping HTTP requests and responses in the simplest way possible, it unifies and distills the API for web servers, web frameworks, and software in between (the so-called middleware) into a single method call.

Affected versions of this package are vulnerable to Incorrect Behavior Order: Validate Before Canonicalize in the Rack::Static component. An attacker can bypass intended security headers by requesting static files using URL-encoded paths, causing the headers not to be applied as expected.

Remediation

Upgrade rack to version 2.2.23, 3.1.21, 3.2.6 or higher.

References

• GitHub Advisory
• GitHub Commit

Overview

rack is a minimal, modular and adaptable interface for developing web applications in Ruby. By wrapping HTTP requests and responses in the simplest way possible, it unifies and distills the API for web servers, web frameworks, and software in between (the so-called middleware) into a single method call.

Affected versions of this package are vulnerable to Permissive Regular Expression in the Rack::Directory component when the configured root path is interpolated directly into a regular expression without escaping. An attacker can obtain sensitive filesystem path information by supplying a root path containing regex metacharacters, which causes the directory listing to reveal unintended details in the HTML output.

Remediation

Upgrade rack to version 2.2.23, 3.1.21, 3.2.6 or higher.

References

• GitHub Advisory
• GitHub Commit

Overview

Affected versions of this package are vulnerable to Uncontrolled Recursion in the Parser class. An attacker can cause a stack overflow or excessive memory consumption by supplying deeply nested CSS blocks or functions.

Remediation

Upgrade crass to version 1.0.7 or higher.

References

• Changelog
• GitHub Advisory
• GitHub Commit
• GitHub Release

Overview

Affected versions of this package are vulnerable to Uncontrolled Recursion when failing to apply :preserve_comments for a stylesheet containing a very large number of adjacent CSS comments. An attacker can cause a stack overflow and crash the application.

Remediation

Upgrade crass to version 1.0.7 or higher.

References

• Changelog
• GitHub Advisory
• GitHub Commit
• GitHub Release

Overview

Affected versions of this package are vulnerable to Uncontrolled Recursion in scanner.rb. An attacker can cause a stack overflow and crash the application by supplying CSS input containing numerous adjacent comments.

Remediation

Upgrade crass to version 1.0.7 or higher.

References

• Changelog
• GitHub Advisory
• GitHub Commit
• GitHub Release

Overview

json is a JSON implementation as a Ruby extension in C.

Affected versions of this package are vulnerable to Heap-based Buffer Overflow via the JSON.dump or JSON::State#generate process when streaming oversized attacker-controlled strings to an IO object. An attacker can cause a process crash or denial of service by providing a specially crafted string near 16 KB in size.

Remediation

Upgrade json to version 2.19.9 or higher.

References

• GitHub Advisory
• GitHub Commit
• GitHub Release

Overview

rack is a minimal, modular and adaptable interface for developing web applications in Ruby. By wrapping HTTP requests and responses in the simplest way possible, it unifies and distills the API for web servers, web frameworks, and software in between (the so-called middleware) into a single method call.

Affected versions of this package are vulnerable to CRLF Injection in the Rack::Multipart::Parser component. An attacker can inject arbitrary HTTP headers or perform response splitting by crafting multipart requests with obs-fold sequences in headers, which are improperly unfolded and preserved in parsed parameter values.

Remediation

Upgrade rack to version 3.2.6 or higher.

References

• GitHub Advisory
• GitHub Commit

Overview

rack is a minimal, modular and adaptable interface for developing web applications in Ruby. By wrapping HTTP requests and responses in the simplest way possible, it unifies and distills the API for web servers, web frameworks, and software in between (the so-called middleware) into a single method call.

Affected versions of this package are vulnerable to Improper Handling of Length Parameter Inconsistency via the Rack::Files#fail component. An attacker can cause incorrect HTTP response framing and potential response desynchronization by requesting a non-existent path containing percent-encoded UTF-8 characters, which leads to a mismatch between the declared and actual Content-Length values.

Remediation

Upgrade rack to version 2.2.23, 3.1.21, 3.2.6 or higher.

References

• GitHub Advisory
• GitHub Commit

Overview

rack is a minimal, modular and adaptable interface for developing web applications in Ruby. By wrapping HTTP requests and responses in the simplest way possible, it unifies and distills the API for web servers, web frameworks, and software in between (the so-called middleware) into a single method call.

Affected versions of this package are vulnerable to Improper Validation of Syntactic Correctness of Input in the Rack::Request component. An attacker can bypass host allowlist checks by supplying specially crafted Host headers containing invalid characters, potentially leading to unauthorized access or manipulation of application behavior by exploiting improper validation during host header parsing.

Remediation

Upgrade rack to version 3.1.21, 3.2.6 or higher.

References

• GitHub Advisory
• GitHub Commit

Overview

rack is a minimal, modular and adaptable interface for developing web applications in Ruby. By wrapping HTTP requests and responses in the simplest way possible, it unifies and distills the API for web servers, web frameworks, and software in between (the so-called middleware) into a single method call.

Affected versions of this package are vulnerable to Interpretation Conflict in the Rack::Multipart::Parser component. An attacker can cause the application to interpret multipart form data differently from upstream proxies or WAFs by sending requests with multiple boundary parameters in the Content-Type header. This can allow malicious form fields or file uploads to bypass upstream inspection and be processed by the application.

Note:

This is only exploitable if an upstream proxy, WAF, or intermediary interprets the first boundary parameter while the application parses the last one.

Remediation

Upgrade rack to version 2.2.23, 3.1.21, 3.2.6 or higher.

References

• GitHub Advisory
• GitHub Advisory

Overview

rack is a minimal, modular and adaptable interface for developing web applications in Ruby. By wrapping HTTP requests and responses in the simplest way possible, it unifies and distills the API for web servers, web frameworks, and software in between (the so-called middleware) into a single method call.

Affected versions of this package are vulnerable to Interpretation Conflict in the forwarded_values component. An attacker can manipulate HTTP headers to inject semicolons into quoted values, causing the process to misinterpret a single quoted value as multiple directives. This can result in host, proto, for, or by parameters being smuggled through a single header value, potentially leading to host and scheme spoofing by sending specially crafted Forwarded headers.

Remediation

Upgrade rack to version 3.1.21, 3.2.6 or higher.

References

• GitHub Advisory
• GitHub Commit

Overview

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) in debug exceptions, which use ERB escaping. An attacker can execute JavaScript in the context of the affected application by triggering a malicious exception message that is rendered bypassing the intended escaping.

Note:

This is only exploitable if detailed exception pages are enabled (config.consider_all_requests_local = true), which they are by default.

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 actionpack to version 8.1.2.1 or higher.

References

• GitHub Advisory
• GitHub Commit
• GitHub Release

Overview

activesupport is a toolkit of support libraries and Ruby core extensions extracted from the Rails framework.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) via the @html_unsafe flag used by the SafeBuffer#% function. An attacker can inject scripts by providing untrusted arguments to the formatting operation after the buffer has been mutated in place, which mayb cause the result to be incorrectly marked as safe and bypass automatic escaping.

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 activesupport to version 7.2.3.1, 8.0.4.1, 8.1.2.1 or higher.

References

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

Overview

loofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) in the SVG sanitizer's handling of the href attribute, which restricts xlink:href on SVG elements to local references but does not apply the same restriction to the plain href attribute that SVG 2 browsers also honor. An attacker can make sanitized SVG reference arbitrary external documents by using a plain href on elements such as <use> or <feImage>, loading external SVG content that can execute scripts when the resource is same-origin and dangerous, or external images for tracking. Exploitation requires the application to sanitize user-supplied SVG with the default allowlist, and modern browsers restrict cross-origin <use> fetches, which limits but does not remove the script-execution risk.

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 loofah to version 2.25.2 or higher.

References

• GitHub Advisory
• GitHub ChangeLog
• GitHub Commit
• Release Notes

Overview

Affected versions of this package are vulnerable to Improper Locking in the release_write_lock() and release_read_lock() functions. An attacker can disrupt synchronization guarantees and exploit data races or cause denial of service by invoking these functions from unauthorized threads or without holding the appropriate lock.

Remediation

Upgrade concurrent-ruby to version 1.3.7 or higher.

References

• GitHub Advisory
• GitHub Commit

Overview

Affected versions of this package are vulnerable to Wrap-around Error in ReentrantReadWriteLock that causes incorrect write locks. An attacker can cause a thread to incorrectly obtain a write lock without exclusivity by repeatedly acquiring the read lock 32,768 times, which overflows the internal counter and bypasses the global writer state. This allows other threads to continue acquiring read locks concurrently, leading to data races and inconsistent reads of shared mutable state.

Remediation

Upgrade concurrent-ruby to version 1.3.7 or higher.

References

• GitHub Advisory
• GitHub Commit

Overview

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) in the sanitization process when SVG reference elements such as <use> or <feImage> are included in the overridden allowed tags. An attacker can execute arbitrary scripts or load external resources by crafting SVG elements with unrestricted href attributes. This is only exploitable if the application's configuration overrides the default allowed tags to include SVG reference elements such as <use> or <feImage>.

Workaround

This vulnerability can be mitigated by removing SVG reference elements (such as use and feImage) from the overridden allowed 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 rails-html-sanitizer to version 1.7.1 or higher.

References

• GitHub Advisory
• GitHub Commit
• GitHub Release

Overview

rack is a minimal, modular and adaptable interface for developing web applications in Ruby. By wrapping HTTP requests and responses in the simplest way possible, it unifies and distills the API for web servers, web frameworks, and software in between (the so-called middleware) into a single method call.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) in Rack::Directory, which automatically provides links to filenames on the filesystem. An attacker who can write files on the target system can cause the execution of JavaScript in the context of the hosting application by naming a file with an executable scheme like javascript: as part of its name, and convincing a user to click the malicious entry in the generated directory listing.

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 rack to version 2.2.22, 3.1.20, 3.2.5 or higher.

References

• GitHub Commit