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7.5

Ammonia library may let attackers run JavaScript

CVE-2026-63430 · published 20 days ago
Summary

The Ammonia HTML‑cleaning library (versions before 3.3.2, 4.0.2 and 4.1.3) can incorrectly handle certain math‑related tags, allowing malicious code to be executed when a user views the cleaned page. If your application enables the math tag, annotation‑xml, and any raw‑text HTML element while blocking the encoding attribute, you should upgrade Ammonia to the fixed versions as soon as possible.

What to do
  • Update debian rust-ammonia to version 4.1.3-1.
  • Update ammonia to version 3.3.2.
  • Update ammonia to version 4.0.2.
  • Update ammonia to version 4.1.3.
Affected software
Ecosystem VendorProductAffected versions
– rust-ammonia ammonia < 3.3.2
Debian:12 debian rust-ammonia All versions
Debian:14 debian rust-ammonia < 4.1.3-1
Fix: upgrade to 4.1.3-1
crates.io – ammonia < 3.3.2
>= 4.0.0, < 4.0.2
>= 4.1.0, < 4.1.3
Fix: upgrade to 3.3.2
Original advisory text
ammonia: mXSS via MathML `annotation-xml` encoding strip
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.
References
Fix within
Internet-facing 14 days
Internal 60 days
  • Not known to be exploited
  • Can be exploited automatically
  • Gives an attacker partial control
Severity
7.5 High
Exploitation
<1% chance of attack within 30 days
Type
CWE-79Cross-site Scripting (XSS)
Timeline
Published15 Oct 2026
Updated4 Nov 2026
First seen15 Oct 2026
Sources
CVE-2026-63430 · NVD
CVE-2026-63430 · MITRE
DEBIAN-CVE-2026-63430 · OSV
GHSA-9jh8-v38h-cvhr · OSV
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