CVE-2026-126063 Nokogiri: Mutation XSS through `noscript` content in Nokogiri's HTML5 serializer
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-126063?
CVE-2026-126063 is a low-severity vulnerability in sparklemotion nokogiri, published on 10 Nov 2026.
Official description
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.
Which versions are affected by CVE-2026-126063?
1 open source package ship an affected version, including nokogiri.
| Package | Affected | Fixed in |
|---|---|---|
nokogiri RubyGems | From 1.12.0 | 1.19.5 |
How do I fix CVE-2026-126063?
Upgrade nokogiri to 1.19.5 or later.
Is CVE-2026-126063 being exploited?
There is no known exploitation of CVE-2026-126063 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-126063, GHSA-4p39-36wj-23h4, UBUNTU-CVE-2026-126063.