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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

2.3 · CVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N · score source

EPSS

• CVE-2026-73491: 0.39% estimated exploitation activity in the next 30 days; percentile 33.69 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary Loofah::HTML5::Scrub.alloweduri? 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 alloweduri? 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…

Published by the source

21 Jul 2026, 15:04 UTC

Last modified by the source

12 Aug 2026, 20:59 UTC

Source last checked

26 Oct 2026, 15:52 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-8whx-365g-h9vv

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# Patch Next advisory brief: CVE-2026-73491

Advisory: Loofah `allowed_uri?` does not detect `javascript:` URIs split by named whitespace character references
IDs: CVE-2026-73491, GHSA-8whx-365g-h9vv
Record: https://patchnext.com/advisories/cve-2026-73491 (revision 1, source checked 26 Oct 2026, 15:52 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 2.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: loofah 2.25.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- RubyGems loofah: affected >= 2.25.0, < 2.25.2; fixed in 2.25.2

## Suggested inspection (read-only)
- RubyGems loofah: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on loofah.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-8whx-365g-h9vv (GitHub-reviewed advisory GHSA-8whx-365g-h9vv lists affected ranges: RubyGems loofah >=2.25.0 <2.25.2)

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