Sparklemotion Nokogiri up to 1.19.4 HTML5 Serializer HTML injection

Summaryinfo

A vulnerability identified as problematic has been detected in Sparklemotion Nokogiri up to 1.19.4. This impacts an unknown function of the component HTML5 Serializer. The manipulation leads to HTML injection. This vulnerability is uniquely identified as CVE-2026-126063. The attack is possible to be carried out remotely. No exploit exists. You should upgrade the affected component.

Detailsinfo

A vulnerability was found in Sparklemotion Nokogiri up to 1.19.4 and classified as problematic. This issue affects some unknown functionality of the component HTML5 Serializer. The manipulation with an unknown input leads to a html injection vulnerability. Using CWE to declare the problem leads to CWE-79. The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Impacted is integrity. The summary by CVE is:

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.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-126063 since 11/10/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. It demands that the victim is doing some kind of user interaction. Neither technical details nor an exploit are publicly available. MITRE ATT&CK project uses the attack technique T1059.007 for this issue.

Upgrading to version 1.19.5 eliminates this vulnerability.

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Productinfo

Vendor

• Sparklemotion

Name

• Nokogiri

Version

• 1.19.0
• 1.19.1
• 1.19.2
• 1.19.3
• 1.19.4

Website

• Product: https://github.com/sparklemotion/nokogiri/

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