CVE-2026-126203
Loofah: Mutation XSS in the HTML5 scrubbers through unescaped attribute values
Loofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri. From 2.21.0 until 2.25.3, Loofah's HTML5 APIs Loofah.html5_fragment, Loofah.html5_document, and the scrub_html5_* methods can emit sanitized output that a browser reparses as different markup when used with Nokogiri before 1.19.5, because those Nokogiri versions do not escape angle brackets in attribute values. MathML can place markup inside an allowed attribute so the reparsed output becomes live HTML. The :strip scrubber is affected in every browser, while :prune and :escape are affected in WebKit browsers. Loofah's HTML4 APIs, Loofah::Helpers.sanitize, :whitewash, rails-html-sanitizer's default configuration, and JRuby are not affected. This issue is fixed in version 2.25.3.
Fixes and workarounds
No remediation reported in collected sources.
Missing remediation information is not evidence that no patch exists.
Affected products and versions
| Product | Versions | Authority |
|---|---|---|
| loofah flavorjones |
>= 2.21.0, < 2.25.3 (affected) | CNA: GitHub_M |
Version ranges are source assertions. Check the vendor advisory and your installed configuration before determining exposure.
CVSS assessments
| Version / score | Vector | Authority |
|---|---|---|
| 3.1 / 6.1 medium |
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N | CNA: GitHub_M |
Exploit evidence
No exploit evidence in collected sources. This is not proof of no exploitation.
References
- https://github.com/flavorjones/loofah/security/advisories/GHSA-h6v6-rg66-fqj4CNA: GitHub_M · x_refsource_CONFIRM
- https://github.com/flavorjones/loofah/pull/324CNA: GitHub_M · x_refsource_MISC
- https://github.com/sparklemotion/nokogiri/pull/3741CNA: GitHub_M · x_refsource_MISC
- https://github.com/flavorjones/loofah/commit/7ba1e7b77e043fb7dc832ef746fcbf83137135e6CNA: GitHub_M · x_refsource_MISC
- https://github.com/sparklemotion/nokogiri/commit/635abc8d65c75d594ddf8957fbfbfd822c2c0dbdCNA: GitHub_M · x_refsource_MISC
- https://github.com/flavorjones/loofah/releases/tag/v2.25.3CNA: GitHub_M · x_refsource_MISC
- https://github.com/sparklemotion/nokogiri/releases/tag/v1.19.5CNA: GitHub_M · x_refsource_MISC
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