Vulnerability · Published Oct 15, 2026 · Assigned by GitHub_M
CVE-2026-63430ammonia: mXSS in ammonia via MathML `annotation-xml` encoding strip
Medium 6.3
In plain English
A medium-severity cross-site scripting in ammonia from rust-ammonia. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 46% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | rust-ammonia | no fix listed | DEBIAN-CVE-2026-63430 |
| Debian:13 | rust-ammonia | no fix listed | DEBIAN-CVE-2026-63430 |
| Debian:14 | rust-ammonia | 4.1.3-1 | DEBIAN-CVE-2026-63430 |
| Ubuntu:22.04:LTS | rust-ammonia | no fix listed | UBUNTU-CVE-2026-63430 |
| Ubuntu:24.04:LTS | rust-ammonia | no fix listed | UBUNTU-CVE-2026-63430 |
| Ubuntu:26.04:LTS | rust-ammonia | no fix listed | UBUNTU-CVE-2026-63430 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| rust-ammonia | ammonia | < 3.3.2>= 4.0.0, < 4.0.2>= 4.1.0, < 4.1.3 |
Weakness: CWE-79 · Vector: 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
References
- https://github.com/rust-ammonia/ammonia/security/advisories/GHSA-9jh8-v38h-cvhr x_refsource_CONFIRM
- https://github.com/rust-ammonia/ammonia/pull/243 x_refsource_MISC
- https://github.com/rust-ammonia/ammonia/pull/244 x_refsource_MISC
- https://github.com/rust-ammonia/ammonia/pull/245 x_refsource_MISC
- https://github.com/rust-ammonia/ammonia/commit/004bf2cee4288f74a6ee619d589e3e90c24c09ca x_refsource_MISC
- https://github.com/rust-ammonia/ammonia/commit/7ac3fd3145236f28857eeecbadb544c8659cba31 x_refsource_MISC
- https://github.com/rust-ammonia/ammonia/commit/b51bf4f9749ed3cd518330105f20a2c39c9ee274 x_refsource_MISC
- https://github.com/rust-ammonia/ammonia/releases/tag/v3.3.2 x_refsource_MISC
- https://github.com/rust-ammonia/ammonia/releases/tag/v4.0.2 x_refsource_MISC
- https://github.com/rust-ammonia/ammonia/releases/tag/v4.1.3 x_refsource_MISC
- https://ivan09999.github.io/ammonia-mxss x_refsource_MISC
- https://rustsec.org/advisories/RUSTSEC-2026-0193.html x_refsource_MISC