ammonia: mXSS in ammonia via MathML `annotation-xml` encoding strip

Summary

CVE	CVE-2026-63430
State	PUBLISHED
Assigner	GitHub_M
Source Priority	CVE Program / NVD first with legacy fallback
Published	2026-10-15 19:17:42 UTC
Updated	2026-10-15 21:17:14 UTC
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.

Risk And Classification

Primary CVSS: v4.0 6.3 MEDIUM from [email protected]

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Problem Types: CWE-79 | CWE-79 CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Version	Source	Type	Score	Severity	Vector
4.0	[email protected]	Secondary	6.3	MEDIUM	`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/E:X/C...`
4.0	CNA	DECLARED	6.3	MEDIUM	`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`

CVSS v4.0 Breakdown

Attack Vector

Network

Attack Complexity

Low

Attack Requirements

Present

Privileges Required

None

User Interaction

None

Confidentiality

None

Integrity

None

Availability

None

Sub Conf.

Low

Sub Integrity

Low

Sub Availability

None

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Vendor Declared Affected Products

Source	Vendor	Product	Version	Platforms
CNA	Rust-ammonia	Ammonia	affected < 3.3.2	Not specified
CNA	Rust-ammonia	Ammonia	affected >= 4.0.0, < 4.0.2	Not specified
CNA	Rust-ammonia	Ammonia	affected >= 4.1.0, < 4.1.3	Not specified

References

Reference	Source	Link	Tags
github.com/rust-ammonia/ammonia/commit/7ac3fd3145236f28857eeecbadb544c86...	[email protected]	github.com
rustsec.org/advisories/RUSTSEC-2026-0193.html	[email protected]	rustsec.org
github.com/rust-ammonia/ammonia/releases/tag/v4.0.2	[email protected]	github.com
github.com/rust-ammonia/ammonia/releases/tag/v4.1.3	[email protected]	github.com
github.com/rust-ammonia/ammonia/releases/tag/v3.3.2	[email protected]	github.com
ivan09999.github.io/ammonia-mxss	[email protected]	ivan09999.github.io
github.com/rust-ammonia/ammonia/pull/243	[email protected]	github.com
github.com/rust-ammonia/ammonia/commit/b51bf4f9749ed3cd518330105f20a2c39...	[email protected]	github.com
github.com/rust-ammonia/ammonia/pull/244	[email protected]	github.com
github.com/rust-ammonia/ammonia/commit/004bf2cee4288f74a6ee619d589e3e90c...	[email protected]	github.com
github.com/rust-ammonia/ammonia/pull/245	[email protected]	github.com
github.com/rust-ammonia/ammonia/security/advisories/GHSA-9jh8-v38h-cvhr	134c704f-9b21-4f2e-91b3-4a467353bcc0	github.com
CVE Program record	CVE.ORG	www.cve.org	canonical
NVD vulnerability detail	NVD	nvd.nist.gov	canonical, analysis

No vendor comments have been submitted for this CVE.

There are currently no legacy QID mappings associated with this CVE.