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CVE-2026-73491

Loofah `allowed_uri?` does not detect `javascript:` URIs split by named whitespace character references

2.3 LowFix available

Loofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri. From 2.25.0 until 2.25.2, Loofah::HTML5::Scrub.allowed_uri? does not reject javascript: URIs whose scheme is split or prefixed with the HTML5 named whitespace character references or . CGI.unescapeHTML leaves those references intact, so allowed_uri? reports the URL safe even though a browser decodes and strips the tab or line feed and executes the resulting javascript: URL. This issue affects only callers that pass HTML-encoded strings directly to allowed_uri?; Loofah's default sanitize() path is not affected. This issue is fixed in version 2.25.2.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
High
Privileges needed
Low
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
None
Availability
None

Exploit likelihood

0.39%Up 0.1 points since Aug 13, 2026
90%50%10%1%

What each source reports

CVE List Score used 2.3

Loofah `allowed_uri?` does not detect `javascript:` URIs split by named whitespace character references

Loofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri. From 2.25.0 until 2.25.2, Loofah::HTML5::Scrub.allowed_uri? does not reject javascript: URIs whose scheme is split or prefixed with the HTML5 named whitespace character references or . CGI.unescapeHTML leaves those references intact, so allowed_uri? reports the URL safe even though a browser decodes and strips the tab or line feed and executes the resulting javascript: URL. This issue affects only callers that pass HTML-encoded strings directly to allowed_uri?; Loofah's default sanitize() path is not affected. This issue is fixed in version 2.25.2.

Record
CVE-2026-73491
CVSS 4.0
2.3 LowCVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
Weakness
CWE-184
Updated
2026-11-02
EUVDEUVD-2026-57628 2.3

Loofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri. From 2.25.0 until 2.25.2, Loofah::HTML5::Scrub.allowed_uri? does not reject javascript: URIs whose scheme is split or prefixed with the HTML5 named whitespace character references or . CGI.unescapeHTML leaves those references intact, so allowed_uri? reports the URL safe even though a browser decodes and strips the tab or line feed and executes the resulting javascript: URL. This issue affects only callers that pass HTML-encoded strings directly to allowed_uri?; Loofah's default sanitize() path is not affected. This issue is fixed in version 2.25.2.

Record
EUVD-2026-57628
CVSS 4.0
2.3 LowCVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
Updated
2026-11-02
GitHub AdvisoriesGHSA-8whx-365g-h9vv 2.3

Loofah `allowed_uri?` does not detect `javascript:` URIs split by named whitespace character references

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.

Record
GHSA-8whx-365g-h9vv
CVSS 4.0
2.3 LowCVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
Weakness
CWE-184
Updated
2026-11-02
NVD 2.3

Loofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri. From 2.25.0 until 2.25.2, Loofah::HTML5::Scrub.allowed_uri? does not reject javascript: URIs whose scheme is split or prefixed with the HTML5 named whitespace character references or . CGI.unescapeHTML leaves those references intact, so allowed_uri? reports the URL safe even though a browser decodes and strips the tab or line feed and executes the resulting javascript: URL. This issue affects only callers that pass HTML-encoded strings directly to allowed_uri?; Loofah's default sanitize() path is not affected. This issue is fixed in version 2.25.2.

Record
CVE-2026-73491
CVSS 4.0
2.3 LowCVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Weakness
CWE-184
Updated
2026-11-02
OSV 2.3

Loofah `allowed_uri?` does not detect `javascript:` URIs split by named whitespace character references

Loofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri. From 2.25.0 until 2.25.2, Loofah::HTML5::Scrub.allowed_uri? does not reject javascript: URIs whose scheme is split or prefixed with the HTML5 named whitespace character references or . CGI.unescapeHTML leaves those references intact, so allowed_uri? reports the URL safe even though a browser decodes and strips the tab or line feed and executes the resulting javascript: URL. This issue affects only callers that pass HTML-encoded strings directly to allowed_uri?; Loofah's default sanitize() path is not affected. This issue is fixed in version 2.25.2.

Record
CVE-2026-73491
CVSS 4.0
2.3 LowCVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
Weakness
CWE-184
Updated
2026-11-02
OSVDEBIAN-CVE-2026-73491 2.3

Loofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri. From 2.25.0 until 2.25.2, Loofah::HTML5::Scrub.allowed_uri? does not reject javascript: URIs whose scheme is split or prefixed with the HTML5 named whitespace character references or . CGI.unescapeHTML leaves those references intact, so allowed_uri? reports the URL safe even though a browser decodes and strips the tab or line feed and executes the resulting javascript: URL. This issue affects only callers that pass HTML-encoded strings directly to allowed_uri?; Loofah's default sanitize() path is not affected. This issue is fixed in version 2.25.2.

Record
DEBIAN-CVE-2026-73491
CVSS 4.0
2.3 LowCVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Updated
2026-11-02
Show 6 moreShow less
OSVGHSA-8whx-365g-h9vv 2.3

Loofah `allowed_uri?` does not detect `javascript:` URIs split by named whitespace character references

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.

Record
GHSA-8whx-365g-h9vv
CVSS 4.0
2.3 LowCVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
Weakness
CWE-184
Updated
2026-11-02
OSVUBUNTU-CVE-2026-73491 2.3

Loofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri. From 2.25.0 until 2.25.2, Loofah::HTML5::Scrub.allowed_uri? does not reject javascript: URIs whose scheme is split or prefixed with the HTML5 named whitespace character references or . CGI.unescapeHTML leaves those references intact, so allowed_uri? reports the URL safe even though a browser decodes and strips the tab or line feed and executes the resulting javascript: URL. This issue affects only callers that pass HTML-encoded strings directly to allowed_uri?; Loofah's default sanitize() path is not affected. This issue is fixed in version 2.25.2.

Record
UBUNTU-CVE-2026-73491
CVSS 4.0
2.3 LowCVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
Updated
2026-11-02
OSVopenSUSE-SU-2026:12153-1 No score

hawk2-2.7.2+git.1792148770.648dcddb-1.1 on GA media

These are all security issues fixed in the hawk2-2.7.2+git.1792148770.648dcddb-1.1 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2026:12153-1
Updated
2026-11-02
OSVopenSUSE-SU-2026:22068-1 No score

Security update for hawk2

This update for hawk2 fixes the following issues:

  • CVE-2026-42246: net-imap: MITM attacker can cause Net::IMAP#starttls to return successfully, without starting TLS (bsc#1268996).
  • CVE-2026-66066: unsafe image processing operations on untrusted uploads can allow arbitrary file reading and remote code execution (bsc#1273348).
  • CVE-2026-71847: json: heap use-after free in JSON::ResumableParser partial_value can lead to crash on truncated duplicate-key streams (bsc#1275213).
  • CVE-2026-73490: loofah: improper handling of SVG attributes in the HTML5 sanitizer allows bypass of local-reference restrictions (bsc#1275179).
  • CVE-2026-73491: loofah: improper handling of javascript: URIs can lead to XSS (bsc#1275183).
  • CVE-2026-73492: loofah: improper handling of javascript: and vbscript: URIs can lead to XSS (bsc#1275188).
  • CVE-2026-73648: rails-html-sanitizer: cross-site scripting is possible when the sanitizer is configured to allow certain SVG reference elements (bsc#1275200).

Changes for hawk2:

  • Update to version 2.7.2+git.1788518533.7d4dadd6 (bsc#1275019):
  • Test: give sle15 more time when choosing between sle15 and sle16
  • Dev: bump jQuery version to 4.0.0
  • Dev: bump jQuery version to 3.5.0
  • Dev: bump jQuery version to 2.2.4
  • Test: update the e2e test for the change allowing custom parameters
  • Dev: enable custom Parameters and Meta Attributes (bsc#1274860)
  • CI/CD: update hawk examiner entry point
  • Test: enable test_add_clone against hawk-apiserver verion 0.2.1
  • Test: fix SyntaxWarning: invalid escape sequence '|'
  • Test: make the tests compatible against hawk-apiserver ver0.2.0
Record
openSUSE-SU-2026:22068-1
Updated
2026-11-02
OSVSUSE-SU-2026:24195-1 No score

Security update for hawk2

This update for hawk2 fixes the following issues:

  • CVE-2026-42246: net-imap: MITM attacker can cause Net::IMAP#starttls to return successfully, without starting TLS (bsc#1268996).
  • CVE-2026-66066: unsafe image processing operations on untrusted uploads can allow arbitrary file reading and remote code execution (bsc#1273348).
  • CVE-2026-71847: json: heap use-after free in JSON::ResumableParser partial_value can lead to crash on truncated duplicate-key streams (bsc#1275213).
  • CVE-2026-73490: loofah: improper handling of SVG attributes in the HTML5 sanitizer allows bypass of local-reference restrictions (bsc#1275179).
  • CVE-2026-73491: loofah: improper handling of javascript: URIs can lead to XSS (bsc#1275183).
  • CVE-2026-73492: loofah: improper handling of javascript: and vbscript: URIs can lead to XSS (bsc#1275188).
  • CVE-2026-73648: rails-html-sanitizer: cross-site scripting is possible when the sanitizer is configured to allow certain SVG reference elements (bsc#1275200).

Changes for hawk2:

  • Update to version 2.7.2+git.1788518533.7d4dadd6 (bsc#1275019):
  • Test: give sle15 more time when choosing between sle15 and sle16
  • Dev: bump jQuery version to 4.0.0
  • Dev: bump jQuery version to 3.5.0
  • Dev: bump jQuery version to 2.2.4
  • Test: update the e2e test for the change allowing custom parameters
  • Dev: enable custom Parameters and Meta Attributes (bsc#1274860)
  • CI/CD: update hawk examiner entry point
  • Test: enable test_add_clone against hawk-apiserver verion 0.2.1
  • Test: fix SyntaxWarning: invalid escape sequence '|'
  • Test: make the tests compatible against hawk-apiserver ver0.2.0
Record
SUSE-SU-2026:24195-1
Updated
2026-11-02
OSVSUSE-SU-2026:24250-1 No score

Security update for hawk2

This update for hawk2 fixes the following issues:

  • CVE-2026-42246: net-imap: MITM attacker can cause Net::IMAP#starttls to return successfully, without starting TLS (bsc#1268996).
  • CVE-2026-66066: unsafe image processing operations on untrusted uploads can allow arbitrary file reading and remote code execution (bsc#1273348).
  • CVE-2026-71847: json: heap use-after free in JSON::ResumableParser partial_value can lead to crash on truncated duplicate-key streams (bsc#1275213).
  • CVE-2026-73490: loofah: improper handling of SVG attributes in the HTML5 sanitizer allows bypass of local-reference restrictions (bsc#1275179).
  • CVE-2026-73491: loofah: improper handling of javascript: URIs can lead to XSS (bsc#1275183).
  • CVE-2026-73492: loofah: improper handling of javascript: and vbscript: URIs can lead to XSS (bsc#1275188).
  • CVE-2026-73648: rails-html-sanitizer: cross-site scripting is possible when the sanitizer is configured to allow certain SVG reference elements (bsc#1275200).

Changes for hawk2:

  • Update to version 2.7.2+git.1788518533.7d4dadd6 (bsc#1275019):
  • Test: give sle15 more time when choosing between sle15 and sle16
  • Dev: bump jQuery version to 4.0.0
  • Dev: bump jQuery version to 3.5.0
  • Dev: bump jQuery version to 2.2.4
  • Test: update the e2e test for the change allowing custom parameters
  • Dev: enable custom Parameters and Meta Attributes (bsc#1274860)
  • CI/CD: update hawk examiner entry point
  • Test: enable test_add_clone against hawk-apiserver verion 0.2.1
  • Test: fix SyntaxWarning: invalid escape sequence '|'
  • Test: make the tests compatible against hawk-apiserver ver0.2.0
Record
SUSE-SU-2026:24250-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
loofah
RubyGems
 2.25.0 up to 2.25.2
2.25.2
ruby-loofah
Debian:12
 All versions, plus listed versions
2.19.1-12.20.0-12.21.3-12.21.4-12.22.0-1
Show 6 moreShow less
2.24.0-12.24.1-12.25.0-12.25.1-12.25.1-22.25.2-1
 None known
ruby-loofah
Debian:13
 All versions, plus listed versions
2.24.0-12.24.1-12.25.0-12.25.1-12.25.1-22.25.2-1
 None known
ruby-loofah
Debian:14
 before 2.25.2-1, plus listed versions
2.24.0-12.24.1-12.25.0-12.25.1-12.25.1-2
2.25.2-1
loofah
RubyGems
 2.25.0 up to 2.25.2, plus listed versions
2.25.1
2.25.2
hawk2
SUSE:Linux Enterprise High Availability Extension 16.0
From an advisory covering 7 CVEs
 before 2.7.2+git.1788518533.7d4dadd6-160000.1.1
2.7.2+git.1788518533.7d4dadd6-160000.1.1
hawk2
SUSE:Linux Enterprise Server for SAP applications 16.0
From an advisory covering 7 CVEs
 before 2.7.2+git.1788518533.7d4dadd6-160000.1.1
2.7.2+git.1788518533.7d4dadd6-160000.1.1
ruby-loofah
Ubuntu:16.04:LTS
 All versions, plus listed versions
2.0.2-12.0.3-12.0.3-22.0.3-2+deb9u1build0.16.04.12.0.3-2+deb9u2build0.16.04.12.0.3-2+deb9u3build0.16.04.1
 None known
ruby-loofah
Ubuntu:18.04:LTS
 All versions, plus listed versions
2.0.3-22.2.2-1
 None known
ruby-loofah
Ubuntu:20.04:LTS
 All versions, plus listed versions
2.2.3-12.3.1+dfsg-12.4.0+dfsg-1
 None known
Show 6 moreShow less
Affected packages
PackageAffectedFixed
ruby-loofah
Ubuntu:22.04:LTS
 All versions, plus listed versions
2.12.0-12.13.0-12.13.0-2
 None known
ruby-loofah
Ubuntu:24.04:LTS
 All versions, plus listed versions
2.21.3-12.21.4-12.22.0-1
 None known
ruby-loofah
Ubuntu:26.10
 All versions, plus listed versions
2.25.0-12.25.1-22.25.2-1
 None known
ruby-loofah
Ubuntu:26.04:LTS
 All versions, plus listed versions
2.24.1-12.25.0-1
 None known
hawk2
openSUSE:Tumbleweed
From an advisory covering 7 CVEs
 before 2.7.2+git.1792148770.648dcddb-1.1
2.7.2+git.1792148770.648dcddb-1.1
hawk2
openSUSE:Leap 16.0
From an advisory covering 7 CVEs
 before 2.7.2+git.1788518533.7d4dadd6-160000.1.1
2.7.2+git.1788518533.7d4dadd6-160000.1.1

History

History
RecordedChangedSources
affected, facts
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-73491 is a low vulnerability (CVSS 2.3) in Flavorjones Loofah, published July 21, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.39%, the 33rd percentile. Fixed in loofah 2.25.2.

References

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