PT-2026-54956 · Crates.Io · Ammonia
Published
2026-06-30
·
Updated
2026-06-30
None
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If a certain set of MathML tags are enabled, an attacker can inject arbitrary JavaScript code into the user's browser.
The
annotation-xml tag has slightly different behavior than the other "integration point"
tags in MathML and SVG, but ammonia didn't handle it, so it didn't correctly
strip the namespace-incompatible tags.This vulnerability only has an effect when the
math and annotation-xml tags
are both enabled, but the encoding attribute is disabled, because it relies
on the following sequence of steps:- User writes code like
<math><annotation-xml encoding="text/html"><gadget></annotation-xml></math>. - Namespace filtering checks the DOM, and it passes.
<gadget>is parsed as HTML. - Attribute filter strips it down to
<math><annotation-xml><gadget></annotation-xml></math>. Because the encoding attribute is gone,<gadget>is now parsed as MathML. - The gadget is written in such a way that it exploits the parsing differences between HTML and MathML.
Additionally, the gadget can only be written using a tag that is parsed as raw text in HTML.
These [elements] are:
- title
- textarea
- xmp
- iframe
- noembed
- noframes
- plaintext
- noscript
- style
- script
Applications that do not explicitly allow any of these tags should not be affected, since none are allowed by default.
[elements]: https://github.com/servo/html5ever/blob/045a0378f2b0f8d4a350793899cf722a2a9b3d11/html5ever/src/tree builder/rules.rs
Discovered by: Ivan Ivančić · Date: 2026-06-29 · Found via local differential analysis and source review of ammonia's sanitisation pipeline; no third-party systems were tested.
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Related Identifiers
Affected Products
Ammonia