RUSTSEC-2026-0193: mXSS in ammonia via MathML annotation-xml

RUSTSEC-2026-0193 Vulnerability Overview mXSS in ammonia via MathML encoding strip Affected Components Package: ammonia (crates.io) Type: Vulnerability Categories: format-injection Keywords: #html #xss Aliases: GHSA-9jh9-v38h-cvhr Fix Patched: >=4.1.3, >=4.0.2, =3.3.2, <4.0.8 Description If certain MathML tags are enabled, an attacker can inject arbitrary JavaScript code into the user's browser. The tag behaves slightly differently from other "integration point" tags in MathML and SVG, but ammonia does not handle it correctly, resulting in failure to properly strip namespace-incompatible tags. This vulnerability only has an impact when both and tags are enabled but the attribute is disabled, as it relies on the following sequence of steps: 1. The user writes code similar to . 2. The namespace filter checks the DOM and passes. is parsed as HTML. 3. The attribute filter strips it down to . Since the encoding attribute is gone, is now parsed as MathML. 4. The gadget is crafted to exploit the differences between HTML and MathML parsing. Furthermore, the gadget can only be written using tags that are parsed as raw text in HTML. These elements include: title textarea xmp iframe noembed noframes plaintext noscript style script Applications that do not explicitly allow any of these tags should not be affected, as they are not allowed by default. Discoverer ivan0912 (YesWeHack) Date 2026-06-29 - ammonia sanitization pipeline discovered via local differential analysis and source code review; third-party systems were not tested. License CCO-1.0

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RUSTSEC-2026-0193: mXSS in ammonia via MathML annotation-xml

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