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CVE-2026-126203

Loofah: Mutation XSS in the HTML5 scrubbers through unescaped attribute values

6.1 mediumFix available

Medium (6.1) in flavorjones loofah. Fixed in loofah 2.25.3.

On this page
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.

Severity

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
CISA's assessment (SSVC)
Exploitation: none · Automatable: no · Technical impact: partial, assessed 2026-11-12. From CISA's Vulnrichment in the CVE List: whether it is exploited, whether exploiting it can be automated, and how much control it gives.
CWEs
CWE-79 Improper Neutralization of Input During Web Page Generation (Cross-site Scripting)
CWE-116 Improper Encoding or Escaping of Output
OWASP Top 10
A05:2025 Injection
Published
Modified
Assigned by
GitHub_M (CNA)
NVD analysis
Awaiting analysis
Record from
the NVD, synced

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Affected

Versions

From the CNA's record in the CVE List.

ProductAffected
flavorjones loofah>= 2.21.0, < 2.25.3

Packages (OSV)

AdvisoryEcosystemPackageAffectedFixed in
GHSA-h6v6-rg66-fqj4RubyGemsloofah>=2.21.0 <2.25.32.25.3

Attack patterns (CAPEC)

  • CAPEC-73 User-Controlled Filename Likelihood: High · Severity: High
  • CAPEC-81 Web Server Logs Tampering Likelihood: Medium · Severity: High
  • CAPEC-85 AJAX Footprinting Likelihood: High · Severity: Low
  • CAPEC-104 Cross Zone Scripting Likelihood: Medium · Severity: High
  • CAPEC-63 Cross-Site Scripting (XSS) Likelihood: High · Severity: Very High
  • CAPEC-209 XSS Using MIME Type Mismatch Severity: Medium
  • CAPEC-588 DOM-Based XSS Likelihood: High · Severity: Very High
  • CAPEC-591 Reflected XSS Likelihood: High · Severity: Very High
  • CAPEC-592 Stored XSS Likelihood: High · Severity: Very High

The attack patterns MITRE's CAPEC relates to this record's weaknesses, as MITRE names them. Credits.

References

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