Bug 2555552

Summary: CVE-2026-63430 python-nh3: ammonia: Cross-site scripting via improper MathML namespace handling [epel-all]
Product: [Fedora] Fedora EPEL Reporter: Marian Rehak <mrehak>
Component: python-nh3Assignee: Mattia Verga <mattia.verga>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: epel10CC: mattia.verga, python-packagers-sig, rust-sig
Target Milestone: ---Keywords: Security, SecurityTracking
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Hardware: Unspecified   
OS: Unspecified   
Whiteboard: {"flaws": ["eae996fb-ceb6-4e94-b9b4-eeb08f15d5ef"]}
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On:    
Bug Blocks: 2553658    

Description Marian Rehak 2026-10-19 11:33:29 UTC 
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.

ammonia is a Rust library for repairing and securing untrusted HTML. Prior to 3.3.2, 4.0.2, and 4.1.3, applications that explicitly allow the math tag, annotation-xml, and at least one raw-text HTML element while disallowing the encoding attribute can permit mutation cross-site scripting. ammonia does not correctly implement annotation-xml's encoding-dependent MathML integration-point behavior after attribute filtering removes encoding, so the sanitizer validates a descendant under one namespace interpretation while the browser reparses the output under another. An attacker can use that namespace transition and an allowed raw-text HTML element to execute JavaScript when a user renders the sanitized output. The required tags are not enabled by default, so applications that do not explicitly allow them are not affected. This issue is fixed in versions 3.3.2, 4.0.2, and 4.1.3.