# CVE-2026-126203: Loofah: Mutation XSS in the HTML5 scrubbers through unescaped attribute values

Status: published. Published: 2026-11-12. Updated: 2026-11-12.

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.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- flavorjones / loofah: >= 2.21.0, < 2.25.3 (affected). Source: CNA: GitHub_M

## Severity and prioritization

- CVSS 3.1: 6.1 (medium); CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N; source: CNA: GitHub_M

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-79, CWE-116

## 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-fqj4 (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/flavorjones/loofah/pull/324 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/sparklemotion/nokogiri/pull/3741 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/flavorjones/loofah/commit/7ba1e7b77e043fb7dc832ef746fcbf83137135e6 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/sparklemotion/nokogiri/commit/635abc8d65c75d594ddf8957fbfbfd822c2c0dbd (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/flavorjones/loofah/releases/tag/v2.25.3 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/sparklemotion/nokogiri/releases/tag/v1.19.5 (CNA: GitHub_M; x_refsource_MISC)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-126203; retrieved 2026-11-12; source updated 2026-11-12

Revision: 0bb59e043026f169d90be997b76951c04dbe9e0fc8445f56ba33603cda684d64

Canonical: https://y2.dev/cve/CVE-2026-126203

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