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CVE-2026-63430— ammonia: mXSS in ammonia via MathML `annotation-xml` encoding strip

Quick assessment

Affected
rust-ammonia ammonia
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Ammonia 是一个用于修复和加固不可信 HTML 的 Rust 库。在版本 3.3.2、4.0.2 和 4.1.3 之前，如果应用程序明确允许使用 标签、 元素以及至少一种原始文本型 HTML 元素，同时禁止使用 属性，则可能导致跨站脚本攻击（XSS）。 具体而言，Ammonia 在属性过滤移除 属性后，未能正确实现 所依赖的 MathML 集成点行为。这导致 sanitizers（过滤器）在一种命名空间解释下对某个后代元素进行验证，而浏览器在重新解析输出时却采用另一种命名空间解释。攻击者可利用这种命名空间转换

CVSS 6.3 · Medium EPSS 0.55% · P45

Affected Version Matrix 3

VendorProduct Version RangeStatus
rust-ammonia ammonia < 3.3.2 affected
>= 4.0.0, < 4.0.2 affected
>= 4.1.0, < 4.1.3 affected
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I. Basic Information for CVE-2026-63430

Vulnerability Information
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Vulnerability Title
ammonia: mXSS in ammonia via MathML `annotation-xml` encoding strip
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
在Web页面生成时对输入的转义处理不恰当(跨站脚本)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
rust-ammonia ammonia < 3.3.2 -

II. Public POCs for CVE-2026-63430

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III. Intelligence Information for CVE-2026-63430

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Patches & Fixes for CVE-2026-63430 (7)

Vendor Advisories for CVE-2026-63430 (2)

Security Blog Posts for CVE-2026-63430 (1)

Vendor Pages for CVE-2026-63430 (1)

Other References for CVE-2026-63430 (1)

IV. Related Vulnerabilities

Same product: ammonia
Same vendor: rust-ammonia
Same weakness: CWE-79

V. Comments for CVE-2026-63430

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