Mistune Math Plugin has an XSS Escape Bypass

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

EPSS

• CVE-2026-44708: 0.23% estimated exploitation activity in the next 30 days; percentile 13.65 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The mistune math plugin renders inline math ($...$) and block math ($$...$$) by concatenating the raw user-supplied content directly into the HTML output without any HTML escaping. This occurs even when the parser is explicitly created with escape=True, which is supposed to guarantee that all user-controlled text is sanitised before reaching the DOM. The result is a silent contract violation: a developer who enables escape=True reasonably expects complete XSS protection, but the math plugin operates as an independent render path that ignores the renderer's escape flag entirely. Details File: src/mistune/plugins/math.py Both functions take text directly from the parsed token and concatenate it into the output string. Neither function: - calls escape(text) from mistune.util - checks renderer.escape - calls safeentity(text) or any other sanitisation helper The escape=True flag only influences the main HTMLRenderer methods (paragraph, heading, codespan, etc.). Plugin render…

Published by the source

8 May 2026, 23:40 UTC

Last modified by the source

10 Sep 2026, 03:51 UTC

Source last checked

26 Oct 2026, 13:45 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-8g87-j6q8-g93x

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-8g87-j6q8-g93x

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# Patch Next advisory brief: CVE-2026-44708

Advisory: Mistune Math Plugin has an XSS Escape Bypass
IDs: CVE-2026-44708, GHSA-8g87-j6q8-g93x
Record: https://patchnext.com/advisories/cve-2026-44708 (revision 2, source checked 26 Oct 2026, 13:45 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI mistune: affected <= 3.2.0

## Suggested inspection (read-only)
- `python -m pip show mistune`: prints the installed version. Run with the environment that serves production active.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on mistune.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-8g87-j6q8-g93x (OSV record GHSA-8g87-j6q8-g93x lists affected ranges: PyPI mistune >=0 <=3.2.0)
- Verified: https://github.com/advisories/GHSA-8g87-j6q8-g93x (GitHub-reviewed advisory GHSA-8g87-j6q8-g93x lists affected ranges: PyPI mistune >=0 <=3.2.0)

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