# ammonia: mXSS via MathML \`annotation-xml\` encoding strip

Advisory record · `GHSA-9jh8-v38h-cvhr`

- **Identifiers:** `GHSA-9jh8-v38h-cvhr` · `CVE-2026-63430` · `RUSTSEC-2026-0193`
- **State:** Confirmed
- **Severity:** CVSS 6.3 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-79](https://cwe.mitre.org/data/definitions/79.html)
- **Tags:** [Cross-site scripting (XSS)](https://agentprime.io/advisories/tag/xss.md)
- **Published:** 22 Oct 2026
- **Updated:** 22 Oct 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 22 Oct 2026, 14:06 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `ammonia` (crates.io): affected `<3.3.2 || >=4.0.0, <4.0.2 || >=4.1.0, <4.1.3`; fixed in `3.3.2`, `4.0.2`, `4.1.3`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> ammonia versions before 3.3.2, from 4.0.0 before 4.0.2, and from 4.1.0 before 4.1.3 are affected. If an application allows the math and annotation-xml tags but not the encoding attribute, and also allows a raw-text tag such as style, an attacker can inject JavaScript into a user's browser. Upgrade to 3.3.2, 4.0.2, or 4.1.3.

Written 3 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 6.3 Medium, CVSS 4.0: `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`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0056, the 46th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:24 UTC: First seen by agentprime
- 31 Oct 2026, 14:24 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-9jh8-v38h-cvhr)

## Sources

- [GitHub Advisory Database: GHSA-9jh8-v38h-cvhr](https://github.com/advisories/GHSA-9jh8-v38h-cvhr)
- [OSV: GHSA-9jh8-v38h-cvhr](https://osv.dev/vulnerability/GHSA-9jh8-v38h-cvhr)
- <https://github.com/rust-ammonia/ammonia/security/advisories/GHSA-9jh8-v38h-cvhr>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-63430>
- <https://github.com/rust-ammonia/ammonia/pull/243>
- <https://github.com/rust-ammonia/ammonia/pull/244>
- <https://github.com/rust-ammonia/ammonia/pull/245>
- <https://github.com/rust-ammonia/ammonia/commit/004bf2cee4288f74a6ee619d589e3e90c24c09ca>
- <https://github.com/rust-ammonia/ammonia/commit/7ac3fd3145236f28857eeecbadb544c8659cba31>
- <https://github.com/rust-ammonia/ammonia/commit/b51bf4f9749ed3cd518330105f20a2c39c9ee274>
- <https://github.com/rust-ammonia/ammonia>
- <https://github.com/rust-ammonia/ammonia/releases/tag/v3.3.2>
- <https://github.com/rust-ammonia/ammonia/releases/tag/v4.0.2>
- <https://github.com/rust-ammonia/ammonia/releases/tag/v4.1.3>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-9jh8-v38h-cvhr>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-9jh8-v38h-cvhr/>. Everything for agents: <https://agentprime.io/llms.txt>.