loofah

Summary

Loofah::HTML5::Scrub.allowed_uri? does not correctly reject javascript: or vbscript: URIs when the scheme is split by a numeric character reference that has no trailing semicolon. A browser decodes such references and resolves the URL to an executable javascript: scheme, while allowed_uri? reports it safe.

This is a bypass of the fix for GHSA-46fp-8f5p-pf2m, which handled numeric character references with a trailing ; (	, 
, 
) but did not cover the forms without semicolons.

Details

allowed_uri? decodes HTML entities with CGI.unescapeHTML, which decodes numeric character references only when they carry a trailing ;. A reference without a semicolon such as &#58 (colon) or &#9 (tab) is left literal, so the scheme-detection check finds no scheme, and the method falls through to its scheme-less path and returns true.

A browser, however, decodes numeric character references even without a trailing semicolon. An encoded colon such as &#58 becomes the : scheme separator, so javascript&#58alert(1) resolves to javascript:alert(1). Encoded whitespace such as &#9 (tab) is decoded and then stripped from the URL, rejoining the surrounding text, so java&#9script:alert(1) also resolves to javascript:alert(1). In both cases the URL executes while allowed_uri? approved it as safe.

Note that Loofah's default sanitize() path is not affected, because Nokogiri decodes or entity-escapes HTML entities during parsing before Loofah evaluates the URI protocol. This issue only affects callers of the public allowed_uri? string-level helper that pass it HTML-encoded strings.

Impact

Callers that validate a user-controlled URL with Loofah::HTML5::Scrub.allowed_uri? and then render the approved value into an href or other browser-interpreted URI attribute may be vulnerable to cross-site scripting (XSS). This includes applications that call allowed_uri? directly, as well as higher-level features built on top of it, such as Action Text 8.2's markdown link validation.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Responsibly reported by GitHub user @MoonFuji.

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah::HTML5::Scrub.allowed_uri? does not correctly reject javascript: URIs when the scheme is split or prefixed by the HTML5 named character references 	 (tab) or 
 (line feed).

This is a bypass of the fix for GHSA-46fp-8f5p-pf2m, which handled the equivalent numeric character references (	, 
, 
) but did not cover the named forms.

Details

allowed_uri? decodes HTML entities with CGI.unescapeHTML, which handles numeric character references but not HTML5 named character references. Payloads like java	script:alert(1) are therefore left intact, so the method does not recognize the javascript: scheme and returns true. A browser, however, decodes 	 and 
 to tab and line feed and strips them from the URL during parsing, producing javascript:alert(1).

	 and 
 are the only relevant named character references: across the HTML5 named-character table, they are the only two that decode to characters the WHATWG URL parser strips from a URL (U+0009 and U+000A; there is no named reference for U+000D).   /   decode to U+00A0, which browsers do not strip, so they aren't usable for this bypass.

Note that Loofah's default sanitize() path is not affected, because Nokogiri decodes or entity-escapes HTML entities during parsing before Loofah evaluates the URI protocol. This issue only affects callers of the public allowed_uri? string-level helper that pass it HTML-encoded strings.

Impact

Callers that validate a user-controlled URL with Loofah::HTML5::Scrub.allowed_uri? and then render the approved value into an href or other browser-interpreted URI attribute may be vulnerable to cross-site scripting (XSS). This includes applications that call allowed_uri? directly, as well as higher-level features built on top of it, such as Action Text 8.2's markdown link validation.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Responsibly reported by GitHub user @connorshea.

Summary

Loofah::HTML5::Scrub.allowed_uri? does not correctly reject javascript: or vbscript: URIs when the scheme is split by a numeric character reference that has no trailing semicolon. A browser decodes such references and resolves the URL to an executable javascript: scheme, while allowed_uri? reports it safe.

This is a bypass of the fix for GHSA-46fp-8f5p-pf2m, which handled numeric character references with a trailing ; (	, 
, 
) but did not cover the forms without semicolons.

Details

allowed_uri? decodes HTML entities with CGI.unescapeHTML, which decodes numeric character references only when they carry a trailing ;. A reference without a semicolon such as &#58 (colon) or &#9 (tab) is left literal, so the scheme-detection check finds no scheme, and the method falls through to its scheme-less path and returns true.

A browser, however, decodes numeric character references even without a trailing semicolon. An encoded colon such as &#58 becomes the : scheme separator, so javascript&#58alert(1) resolves to javascript:alert(1). Encoded whitespace such as &#9 (tab) is decoded and then stripped from the URL, rejoining the surrounding text, so java&#9script:alert(1) also resolves to javascript:alert(1). In both cases the URL executes while allowed_uri? approved it as safe.

Note that Loofah's default sanitize() path is not affected, because Nokogiri decodes or entity-escapes HTML entities during parsing before Loofah evaluates the URI protocol. This issue only affects callers of the public allowed_uri? string-level helper that pass it HTML-encoded strings.

Impact

Callers that validate a user-controlled URL with Loofah::HTML5::Scrub.allowed_uri? and then render the approved value into an href or other browser-interpreted URI attribute may be vulnerable to cross-site scripting (XSS). This includes applications that call allowed_uri? directly, as well as higher-level features built on top of it, such as Action Text 8.2's markdown link validation.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Responsibly reported by GitHub user @MoonFuji.

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah::HTML5::Scrub.allowed_uri? does not correctly reject javascript: URIs when the scheme is split or prefixed by the HTML5 named character references 	 (tab) or 
 (line feed).

This is a bypass of the fix for GHSA-46fp-8f5p-pf2m, which handled the equivalent numeric character references (	, 
, 
) but did not cover the named forms.

Details

allowed_uri? decodes HTML entities with CGI.unescapeHTML, which handles numeric character references but not HTML5 named character references. Payloads like java	script:alert(1) are therefore left intact, so the method does not recognize the javascript: scheme and returns true. A browser, however, decodes 	 and 
 to tab and line feed and strips them from the URL during parsing, producing javascript:alert(1).

	 and 
 are the only relevant named character references: across the HTML5 named-character table, they are the only two that decode to characters the WHATWG URL parser strips from a URL (U+0009 and U+000A; there is no named reference for U+000D).   /   decode to U+00A0, which browsers do not strip, so they aren't usable for this bypass.

Note that Loofah's default sanitize() path is not affected, because Nokogiri decodes or entity-escapes HTML entities during parsing before Loofah evaluates the URI protocol. This issue only affects callers of the public allowed_uri? string-level helper that pass it HTML-encoded strings.

Impact

Callers that validate a user-controlled URL with Loofah::HTML5::Scrub.allowed_uri? and then render the approved value into an href or other browser-interpreted URI attribute may be vulnerable to cross-site scripting (XSS). This includes applications that call allowed_uri? directly, as well as higher-level features built on top of it, such as Action Text 8.2's markdown link validation.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Responsibly reported by GitHub user @connorshea.

Summary

Loofah::HTML5::Scrub.allowed_uri? does not correctly reject javascript: URIs when the scheme is split by HTML entity-encoded control characters such as 
 (carriage return), 
 (line feed), or 	 (tab).

Details

The allowed_uri? method strips literal control characters before decoding HTML entities. Payloads like java
script:alert(1) survive the control character strip, then 
 is decoded to a carriage return, producing java\rscript:alert(1).

Note that the Loofah sanitizer's default sanitize() path is not affected because Nokogiri decodes HTML entities during parsing before Loofah evaluates the URI protocol. This issue only affects direct callers of the allowed_uri? string-level helper when passing HTML-encoded strings.

Impact

Applications that call Loofah::HTML5::Scrub.allowed_uri? to validate user-controlled URLs and then render approved URLs into href or other browser-interpreted URI attributes may be vulnerable to cross-site scripting (XSS).

This only affects Loofah 2.25.0.

Mitigation

Upgrade to Loofah >= 2.25.1.

Credit

Responsibly reported by HackOne user @smlee.

Summary

Loofah::HTML5::Scrub.allowed_uri? does not correctly reject javascript: URIs when the scheme is split by HTML entity-encoded control characters such as 
 (carriage return), 
 (line feed), or 	 (tab).

Details

The allowed_uri? method strips literal control characters before decoding HTML entities. Payloads like java
script:alert(1) survive the control character strip, then 
 is decoded to a carriage return, producing java\rscript:alert(1).

Note that the Loofah sanitizer's default sanitize() path is not affected because Nokogiri decodes HTML entities during parsing before Loofah evaluates the URI protocol. This issue only affects direct callers of the allowed_uri? string-level helper when passing HTML-encoded strings.

Impact

Applications that call Loofah::HTML5::Scrub.allowed_uri? to validate user-controlled URLs and then render approved URLs into href or other browser-interpreted URI attributes may be vulnerable to cross-site scripting (XSS).

This only affects Loofah 2.25.0.

Mitigation

Upgrade to Loofah >= 2.25.1.

Credit

Responsibly reported by HackOne user @smlee.

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah >= 2.2.0, < 2.19.1 uses recursion for sanitizing CDATA sections, making it susceptible to stack exhaustion and raising a SystemStackError exception. This may lead to a denial of service through CPU resource consumption.

Mitigation

Upgrade to Loofah >= 2.19.1.

Users who are unable to upgrade may be able to mitigate this vulnerability by limiting the length of the strings that are sanitized.

Severity

The Loofah maintainers have evaluated this as High Severity 7.5 (CVSS3.1).

References

• CWE - CWE-674: Uncontrolled Recursion (4.9)

Summary

Loofah >= 2.1.0, < 2.19.1 is vulnerable to cross-site scripting via the image/svg+xml media type in data URIs.

Mitigation

Upgrade to Loofah >= 2.19.1.

Severity

The Loofah maintainers have evaluated this as Medium Severity 6.1.

References

• CWE - CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (4.9)
• SVG MIME Type (image/svg+xml) is misleading to developers · Issue #266 · w3c/svgwg
• https://hackerone.com/reports/1694173
• https://github.com/flavorjones/loofah/issues/101

Credit

This vulnerability was responsibly reported by Maciej Piechota (@haqpl).

Summary

Loofah < 2.19.1 contains an inefficient regular expression that is susceptible to excessive backtracking when attempting to sanitize certain SVG attributes. This may lead to a denial of service through CPU resource consumption.

Mitigation

Upgrade to Loofah >= 2.19.1.

Severity

The Loofah maintainers have evaluated this as High Severity 7.5 (CVSS3.1).

References

• CWE - CWE-1333: Inefficient Regular Expression Complexity (4.9)
• https://hackerone.com/reports/1684163

Credit

This vulnerability was responsibly reported by @ooooooo-q (https://github.com/ooooooo-q).

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah >= 2.2.0, < 2.19.1 uses recursion for sanitizing CDATA sections, making it susceptible to stack exhaustion and raising a SystemStackError exception. This may lead to a denial of service through CPU resource consumption.

Mitigation

Upgrade to Loofah >= 2.19.1.

Users who are unable to upgrade may be able to mitigate this vulnerability by limiting the length of the strings that are sanitized.

Severity

The Loofah maintainers have evaluated this as High Severity 7.5 (CVSS3.1).

References

• CWE - CWE-674: Uncontrolled Recursion (4.9)

Summary

Loofah >= 2.1.0, < 2.19.1 is vulnerable to cross-site scripting via the image/svg+xml media type in data URIs.

Mitigation

Upgrade to Loofah >= 2.19.1.

Severity

The Loofah maintainers have evaluated this as Medium Severity 6.1.

References

• CWE - CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (4.9)
• SVG MIME Type (image/svg+xml) is misleading to developers · Issue #266 · w3c/svgwg
• https://hackerone.com/reports/1694173
• https://github.com/flavorjones/loofah/issues/101

Credit

This vulnerability was responsibly reported by Maciej Piechota (@haqpl).

Summary

Loofah < 2.19.1 contains an inefficient regular expression that is susceptible to excessive backtracking when attempting to sanitize certain SVG attributes. This may lead to a denial of service through CPU resource consumption.

Mitigation

Upgrade to Loofah >= 2.19.1.

Severity

The Loofah maintainers have evaluated this as High Severity 7.5 (CVSS3.1).

References

• CWE - CWE-1333: Inefficient Regular Expression Complexity (4.9)
• https://hackerone.com/reports/1684163

Credit

This vulnerability was responsibly reported by @ooooooo-q (https://github.com/ooooooo-q).

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah >= 2.2.0, < 2.19.1 uses recursion for sanitizing CDATA sections, making it susceptible to stack exhaustion and raising a SystemStackError exception. This may lead to a denial of service through CPU resource consumption.

Mitigation

Upgrade to Loofah >= 2.19.1.

Users who are unable to upgrade may be able to mitigate this vulnerability by limiting the length of the strings that are sanitized.

Severity

The Loofah maintainers have evaluated this as High Severity 7.5 (CVSS3.1).

References

• CWE - CWE-674: Uncontrolled Recursion (4.9)

Summary

Loofah >= 2.1.0, < 2.19.1 is vulnerable to cross-site scripting via the image/svg+xml media type in data URIs.

Mitigation

Upgrade to Loofah >= 2.19.1.

Severity

The Loofah maintainers have evaluated this as Medium Severity 6.1.

References

• CWE - CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (4.9)
• SVG MIME Type (image/svg+xml) is misleading to developers · Issue #266 · w3c/svgwg
• https://hackerone.com/reports/1694173
• https://github.com/flavorjones/loofah/issues/101

Credit

This vulnerability was responsibly reported by Maciej Piechota (@haqpl).

Summary

Loofah < 2.19.1 contains an inefficient regular expression that is susceptible to excessive backtracking when attempting to sanitize certain SVG attributes. This may lead to a denial of service through CPU resource consumption.

Mitigation

Upgrade to Loofah >= 2.19.1.

Severity

The Loofah maintainers have evaluated this as High Severity 7.5 (CVSS3.1).

References

• CWE - CWE-1333: Inefficient Regular Expression Complexity (4.9)
• https://hackerone.com/reports/1684163

Credit

This vulnerability was responsibly reported by @ooooooo-q (https://github.com/ooooooo-q).

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah >= 2.2.0, < 2.19.1 uses recursion for sanitizing CDATA sections, making it susceptible to stack exhaustion and raising a SystemStackError exception. This may lead to a denial of service through CPU resource consumption.

Mitigation

Upgrade to Loofah >= 2.19.1.

Users who are unable to upgrade may be able to mitigate this vulnerability by limiting the length of the strings that are sanitized.

Severity

The Loofah maintainers have evaluated this as High Severity 7.5 (CVSS3.1).

References

• CWE - CWE-674: Uncontrolled Recursion (4.9)

Summary

Loofah >= 2.1.0, < 2.19.1 is vulnerable to cross-site scripting via the image/svg+xml media type in data URIs.

Mitigation

Upgrade to Loofah >= 2.19.1.

Severity

The Loofah maintainers have evaluated this as Medium Severity 6.1.

References

• CWE - CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (4.9)
• SVG MIME Type (image/svg+xml) is misleading to developers · Issue #266 · w3c/svgwg
• https://hackerone.com/reports/1694173
• https://github.com/flavorjones/loofah/issues/101

Credit

This vulnerability was responsibly reported by Maciej Piechota (@haqpl).

Summary

Loofah < 2.19.1 contains an inefficient regular expression that is susceptible to excessive backtracking when attempting to sanitize certain SVG attributes. This may lead to a denial of service through CPU resource consumption.

Mitigation

Upgrade to Loofah >= 2.19.1.

Severity

The Loofah maintainers have evaluated this as High Severity 7.5 (CVSS3.1).

References

• CWE - CWE-1333: Inefficient Regular Expression Complexity (4.9)
• https://hackerone.com/reports/1684163

Credit

This vulnerability was responsibly reported by @ooooooo-q (https://github.com/ooooooo-q).

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah >= 2.2.0, < 2.19.1 uses recursion for sanitizing CDATA sections, making it susceptible to stack exhaustion and raising a SystemStackError exception. This may lead to a denial of service through CPU resource consumption.

Mitigation

Upgrade to Loofah >= 2.19.1.

Users who are unable to upgrade may be able to mitigate this vulnerability by limiting the length of the strings that are sanitized.

Severity

The Loofah maintainers have evaluated this as High Severity 7.5 (CVSS3.1).

References

• CWE - CWE-674: Uncontrolled Recursion (4.9)

Summary

Loofah >= 2.1.0, < 2.19.1 is vulnerable to cross-site scripting via the image/svg+xml media type in data URIs.

Mitigation

Upgrade to Loofah >= 2.19.1.

Severity

The Loofah maintainers have evaluated this as Medium Severity 6.1.

References

• CWE - CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (4.9)
• SVG MIME Type (image/svg+xml) is misleading to developers · Issue #266 · w3c/svgwg
• https://hackerone.com/reports/1694173
• https://github.com/flavorjones/loofah/issues/101

Credit

This vulnerability was responsibly reported by Maciej Piechota (@haqpl).

Summary

Loofah < 2.19.1 contains an inefficient regular expression that is susceptible to excessive backtracking when attempting to sanitize certain SVG attributes. This may lead to a denial of service through CPU resource consumption.

Mitigation

Upgrade to Loofah >= 2.19.1.

Severity

The Loofah maintainers have evaluated this as High Severity 7.5 (CVSS3.1).

References

• CWE - CWE-1333: Inefficient Regular Expression Complexity (4.9)
• https://hackerone.com/reports/1684163

Credit

This vulnerability was responsibly reported by @ooooooo-q (https://github.com/ooooooo-q).

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah >= 2.2.0, < 2.19.1 uses recursion for sanitizing CDATA sections, making it susceptible to stack exhaustion and raising a SystemStackError exception. This may lead to a denial of service through CPU resource consumption.

Mitigation

Upgrade to Loofah >= 2.19.1.

Users who are unable to upgrade may be able to mitigate this vulnerability by limiting the length of the strings that are sanitized.

Severity

The Loofah maintainers have evaluated this as High Severity 7.5 (CVSS3.1).

References

• CWE - CWE-674: Uncontrolled Recursion (4.9)

Summary

Loofah >= 2.1.0, < 2.19.1 is vulnerable to cross-site scripting via the image/svg+xml media type in data URIs.

Mitigation

Upgrade to Loofah >= 2.19.1.

Severity

The Loofah maintainers have evaluated this as Medium Severity 6.1.

References

• CWE - CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (4.9)
• SVG MIME Type (image/svg+xml) is misleading to developers · Issue #266 · w3c/svgwg
• https://hackerone.com/reports/1694173
• https://github.com/flavorjones/loofah/issues/101

Credit

This vulnerability was responsibly reported by Maciej Piechota (@haqpl).

Summary

Loofah < 2.19.1 contains an inefficient regular expression that is susceptible to excessive backtracking when attempting to sanitize certain SVG attributes. This may lead to a denial of service through CPU resource consumption.

Mitigation

Upgrade to Loofah >= 2.19.1.

Severity

The Loofah maintainers have evaluated this as High Severity 7.5 (CVSS3.1).

References

• CWE - CWE-1333: Inefficient Regular Expression Complexity (4.9)
• https://hackerone.com/reports/1684163

Credit

This vulnerability was responsibly reported by @ooooooo-q (https://github.com/ooooooo-q).

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah >= 2.2.0, < 2.19.1 uses recursion for sanitizing CDATA sections, making it susceptible to stack exhaustion and raising a SystemStackError exception. This may lead to a denial of service through CPU resource consumption.

Mitigation

Upgrade to Loofah >= 2.19.1.

Users who are unable to upgrade may be able to mitigate this vulnerability by limiting the length of the strings that are sanitized.

Severity

The Loofah maintainers have evaluated this as High Severity 7.5 (CVSS3.1).

References

• CWE - CWE-674: Uncontrolled Recursion (4.9)

Summary

Loofah >= 2.1.0, < 2.19.1 is vulnerable to cross-site scripting via the image/svg+xml media type in data URIs.

Mitigation

Upgrade to Loofah >= 2.19.1.

Severity

The Loofah maintainers have evaluated this as Medium Severity 6.1.

References

• CWE - CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (4.9)
• SVG MIME Type (image/svg+xml) is misleading to developers · Issue #266 · w3c/svgwg
• https://hackerone.com/reports/1694173
• https://github.com/flavorjones/loofah/issues/101

Credit

This vulnerability was responsibly reported by Maciej Piechota (@haqpl).

Summary

Loofah < 2.19.1 contains an inefficient regular expression that is susceptible to excessive backtracking when attempting to sanitize certain SVG attributes. This may lead to a denial of service through CPU resource consumption.

Mitigation

Upgrade to Loofah >= 2.19.1.

Severity

The Loofah maintainers have evaluated this as High Severity 7.5 (CVSS3.1).

References

• CWE - CWE-1333: Inefficient Regular Expression Complexity (4.9)
• https://hackerone.com/reports/1684163

Credit

This vulnerability was responsibly reported by @ooooooo-q (https://github.com/ooooooo-q).

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah >= 2.2.0, < 2.19.1 uses recursion for sanitizing CDATA sections, making it susceptible to stack exhaustion and raising a SystemStackError exception. This may lead to a denial of service through CPU resource consumption.

Mitigation

Upgrade to Loofah >= 2.19.1.

Users who are unable to upgrade may be able to mitigate this vulnerability by limiting the length of the strings that are sanitized.

Severity

The Loofah maintainers have evaluated this as High Severity 7.5 (CVSS3.1).

References

• CWE - CWE-674: Uncontrolled Recursion (4.9)

Summary

Loofah >= 2.1.0, < 2.19.1 is vulnerable to cross-site scripting via the image/svg+xml media type in data URIs.

Mitigation

Upgrade to Loofah >= 2.19.1.

Severity

The Loofah maintainers have evaluated this as Medium Severity 6.1.

References

• CWE - CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (4.9)
• SVG MIME Type (image/svg+xml) is misleading to developers · Issue #266 · w3c/svgwg
• https://hackerone.com/reports/1694173
• https://github.com/flavorjones/loofah/issues/101

Credit

This vulnerability was responsibly reported by Maciej Piechota (@haqpl).

Summary

Loofah < 2.19.1 contains an inefficient regular expression that is susceptible to excessive backtracking when attempting to sanitize certain SVG attributes. This may lead to a denial of service through CPU resource consumption.

Mitigation

Upgrade to Loofah >= 2.19.1.

Severity

The Loofah maintainers have evaluated this as High Severity 7.5 (CVSS3.1).

References

• CWE - CWE-1333: Inefficient Regular Expression Complexity (4.9)
• https://hackerone.com/reports/1684163

Credit

This vulnerability was responsibly reported by @ooooooo-q (https://github.com/ooooooo-q).

Summary

Loofah's HTML5 sanitizer restricted only the xlink:href attribute on certain SVG elements to local, same-document references. Browsers also accept a plain href attribute as an alternative to the deprecated xlink:href per the SVG 2 spec, but Loofah did not apply the same restriction to it, allowing those elements to reference arbitrary external documents.

Impact

SVG <use> can load and render external SVG content by reference. If the referenced external SVG is same-origin and contains scripts or other dangerous content, it could execute in the context of the sanitized document. <feImage> can load external images, which can be used for tracking. Modern browsers restrict cross-origin <use> fetches, which limits but does not eliminate the risk.

Applications that sanitize user-supplied SVG (directly, or as part of HTML) with Loofah's default allowlist are affected.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Found by the maintainer, Mike Dalessio, during a security audit.

Summary

Loofah >= 2.2.0, < 2.19.1 uses recursion for sanitizing CDATA sections, making it susceptible to stack exhaustion and raising a SystemStackError exception. This may lead to a denial of service through CPU resource consumption.

Mitigation

Upgrade to Loofah >= 2.19.1.

Users who are unable to upgrade may be able to mitigate this vulnerability by limiting the length of the strings that are sanitized.

Severity

The Loofah maintainers have evaluated this as High Severity 7.5 (CVSS3.1).

References

• CWE - CWE-674: Uncontrolled Recursion (4.9)

Summary

Loofah >= 2.1.0, < 2.19.1 is vulnerable to cross-site scripting via the image/svg+xml media type in data URIs.

Mitigation

Upgrade to Loofah >= 2.19.1.

Severity

The Loofah maintainers have evaluated this as Medium Severity 6.1.

References

• CWE - CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (4.9)
• SVG MIME Type (image/svg+xml) is misleading to developers · Issue #266 · w3c/svgwg
• https://hackerone.com/reports/1694173
• https://github.com/flavorjones/loofah/issues/101

Credit

This vulnerability was responsibly reported by Maciej Piechota (@haqpl).

Summary

Loofah < 2.19.1 contains an inefficient regular expression that is susceptible to excessive backtracking when attempting to sanitize certain SVG attributes. This may lead to a denial of service through CPU resource consumption.

Mitigation

Upgrade to Loofah >= 2.19.1.

Severity

The Loofah maintainers have evaluated this as High Severity 7.5 (CVSS3.1).

References

• CWE - CWE-1333: Inefficient Regular Expression Complexity (4.9)
• https://hackerone.com/reports/1684163

Credit

This vulnerability was responsibly reported by @ooooooo-q (https://github.com/ooooooo-q).