CVE-2026-63430ammonia: mXSS in ammonia 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.

CVSS

6.3 MEDIUM (v4.0, CNA)CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

Weakness (CWE)

CWE-79

Known exploited

Not in CISA's KEV catalog

EPSS (exploitation in the next 30 days)

Not loaded for this CVE

Assigned by

GitHub_M

NVD analysis

Awaiting Analysis

Record last updated

Oct 15, 2026

First seen by InfoSec Signals

Oct 15, 2026

The CVE record on cve.org · NVD's entry

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