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

2.3 lowEPSS 0.6%Fix available

Low (2.3) in sparklemotion nokogiri. EPSS 0.6% estimated probability of exploitation activity in the next 30 days. Fixed in nokogiri 1.19.5.

On this page
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.

Severity

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
EPSS
0.6% estimated probability of exploitation activity in the next 30 days; 47th percentile. Scored 2026-11-13. A forecast for this CVE across the internet, not for your own systems.
CISA's assessment (SSVC)
Exploitation: none · Automatable: no · Technical impact: partial, assessed 2026-11-13. 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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CVE-2026-126063

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Affected

Versions

From the CNA's record in the CVE List.

ProductAffected
sparklemotion nokogiri>= 1.12.0, < 1.19.5

Fix and patched versions

  • nokogiri (RubyGems): fixed in 1.19.5

Packages (OSV)

AdvisoryEcosystemPackageAffectedFixed in
GHSA-4p39-36wj-23h4RubyGemsnokogiri>=1.12.0 <1.19.51.19.5

Linux distributions

DistributionReleasePackageFixed inAdvisory
Debian12, 13, 14ruby-nokogirino fix listedDEBIAN-CVE-2026-126063
Ubuntu16.04:LTS, 18.04:LTS, 24.04:LTS and 5 moreruby-nokogirino fix listedUBUNTU-CVE-2026-126063
Azure Linux3rubygem-nokogirino fix listedAZL-113627

From the distributions' data via OSV.dev: the Debian Security Tracker; Ubuntu Security Notices © Canonical Ltd., CC BY-SA 4.0; Microsoft's Azure Linux vulnerability data, MIT. Modified: reformatted and linked to CVE records. Credits. On the distributions' own pages: Debian · Ubuntu.

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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