# CVE-2026-126063: Nokogiri: Mutation XSS through `noscript` content in Nokogiri's HTML5 serializer

Status: published. Published: 2026-11-10. Updated: 2026-11-13.

Nokogiri is an open source XML and HTML library for the Ruby programming language. From 1.12.0 until 1.19.5, the C extension on CRuby and TruffleRuby has a Nokogiri::HTML5 serializer that does not escape text inside noscript elements or angle brackets inside attribute values. When an application sanitizes untrusted HTML with the default parsing options, allows noscript, and sends serialized output to a scripting-enabled browser, the browser can parse markup that Nokogiri did not produce, enabling mutation cross-site scripting. Using parse_noscript_content_as_text: true is the recommended workaround, not the vulnerable default. JRuby is not affected because it does not implement Nokogiri::HTML5. This issue is fixed in version 1.19.5.

## Remediation

- fix: nokogiri (rubygems): GitHub reports patched versions 1.19.5. Check the advisory for the affected release branch. (source: GitHub GHSA-4p39-36wj-23h4) — https://github.com/sparklemotion/nokogiri/security/advisories/GHSA-4p39-36wj-23h4
- fix: nokogiri (RubyGems): OSV reports a fixed version 1.19.5. Check the advisory for supported release branches. (source: OSV GHSA-4p39-36wj-23h4) — https://github.com/advisories/GHSA-4p39-36wj-23h4

## Affected products and versions

- sparklemotion / nokogiri: >= 1.12.0, < 1.19.5 (affected). Source: CNA: GitHub_M
-  / nokogiri (nokogiri): >= 1.12.0, < 1.19.5 (affected, GitHub advisory range). Source: GitHub GHSA-4p39-36wj-23h4
-  / nokogiri (nokogiri): 1.12.0 (affected, RubyGems); 1.12.1 (affected, RubyGems); 1.12.2 (affected, RubyGems); 1.12.3 (affected, RubyGems); 1.12.4 (affected, RubyGems); 1.12.5 (affected, RubyGems); 1.13.0 (affected, RubyGems); 1.13.1 (affected, RubyGems); 1.13.10 (affected, RubyGems); 1.13.2 (affected, RubyGems); 1.13.3 (affected, RubyGems); 1.13.4 (affected, RubyGems); 1.13.5 (affected, RubyGems); 1.13.6 (affected, RubyGems); 1.13.7 (affected, RubyGems); 1.13.8 (affected, RubyGems); 1.13.9 (affected, RubyGems); 1.14.0 (affected, RubyGems); 1.14.0.rc1 (affected, RubyGems); 1.14.1 (affected, RubyGems); 1.14.2 (affected, RubyGems); 1.14.3 (affected, RubyGems); 1.14.4 (affected, RubyGems); 1.14.5 (affected, RubyGems); 1.15.0 (affected, RubyGems); 1.15.1 (affected, RubyGems); 1.15.2 (affected, RubyGems); 1.15.3 (affected, RubyGems); 1.15.4 (affected, RubyGems); 1.15.5 (affected, RubyGems); 1.15.6 (affected, RubyGems); 1.15.7 (affected, RubyGems); 1.16.0 (affected, RubyGems); 1.16.0.rc1 (affected, RubyGems); 1.16.1 (affected, RubyGems); 1.16.2 (affected, RubyGems); 1.16.3 (affected, RubyGems); 1.16.4 (affected, RubyGems); 1.16.5 (affected, RubyGems); 1.16.6 (affected, RubyGems); 1.16.7 (affected, RubyGems); 1.16.8 (affected, RubyGems); 1.17.0 (affected, RubyGems); 1.17.1 (affected, RubyGems); 1.17.2 (affected, RubyGems); 1.18.0 (affected, RubyGems); 1.18.0.rc1 (affected, RubyGems); 1.18.1 (affected, RubyGems); 1.18.10 (affected, RubyGems); 1.18.2 (affected, RubyGems); 1.18.3 (affected, RubyGems); 1.18.4 (affected, RubyGems); 1.18.5 (affected, RubyGems); 1.18.6 (affected, RubyGems); 1.18.7 (affected, RubyGems); 1.18.8 (affected, RubyGems); 1.18.9 (affected, RubyGems); 1.19.0 (affected, RubyGems); 1.19.1 (affected, RubyGems); 1.19.2 (affected, RubyGems); 1.19.3 (affected, RubyGems); 1.19.4 (affected, RubyGems); Ecosystem version events: introduced 1.12.0; fixed 1.19.5. Source: OSV GHSA-4p39-36wj-23h4

## Severity and prioritization

- CVSS 4.0: 2.3 (low); CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N; source: CNA: GitHub_M

- CVSS 4.0: 2.3 (low); CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/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; source: NVD: security-advisories@github.com

- CISA KEV: No listing in collected sources

- EPSS: 0.56% as of 2026-11-13; percentile 47.24%

- 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/sparklemotion/nokogiri/security/advisories/GHSA-4p39-36wj-23h4 (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/sparklemotion/nokogiri/pull/3752 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/sparklemotion/nokogiri/commit/3e84df6ff7ab4d78f446e3a415430bd69a055d32 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/sparklemotion/nokogiri/commit/c6c0bffbdcd194694995acafeeed27326b0805f8 (CNA: GitHub_M; x_refsource_MISC)

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

- https://github.com/sparklemotion/nokogiri/commit/3e84df6ff7ab4d78f446e3a415430bd69a055d32 (security-advisories@github.com)

- https://github.com/sparklemotion/nokogiri/commit/c6c0bffbdcd194694995acafeeed27326b0805f8 (security-advisories@github.com)

- https://github.com/sparklemotion/nokogiri/pull/3752 (security-advisories@github.com)

- https://github.com/sparklemotion/nokogiri/releases/tag/v1.19.5 (security-advisories@github.com)

- https://github.com/sparklemotion/nokogiri/security/advisories/GHSA-4p39-36wj-23h4 (security-advisories@github.com)

- https://github.com/sparklemotion/nokogiri/security/advisories/GHSA-4p39-36wj-23h4 (GitHub Security Advisories; advisory)

- https://github.com/advisories/GHSA-4p39-36wj-23h4 (OSV / GitHub Security Advisories; advisory)

- https://osv.dev/vulnerability/GHSA-4p39-36wj-23h4 (OSV / GitHub Security Advisories; osv)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-126063; retrieved 2026-11-13; source updated 2026-11-13

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-126063; retrieved 2026-11-13; source updated 2026-11-13

- GitHub Security Advisories: https://github.com/sparklemotion/nokogiri/security/advisories/GHSA-4p39-36wj-23h4; retrieved 2026-11-13; source updated 2026-11-10

- OSV / GitHub Security Advisories: https://osv.dev/vulnerability/GHSA-4p39-36wj-23h4; retrieved 2026-11-10; source updated 2026-11-10

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-126063; retrieved 2026-11-13; source updated Not reported

Revision: 0b087c5f23ffdc3a87148a2e42528271d2649c9c90894b96455f06077601894b

Canonical: https://y2.dev/cve/CVE-2026-126063

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