Mistune has XSS via unescaped figclass/figwidth in Figure directive

Exploitation

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

CVSS 4.0

5.3 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N · score source

EPSS

• CVE-2026-44896: 0.20% estimated exploitation activity in the next 30 days; percentile 9.69 (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.

In src/mistune/directives/image.py, the renderfigure() function concatenates figclass and figwidth options directly into HTML attributes without escaping (lines 152-168). This allows attribute injection and XSS even when HTMLRenderer(escape=True) is used, because these values bypass the inline renderer. Other attributes in the same file (src, alt, style) are properly escaped; figclass/figwidth were missed.

Published by the source

8 May 2026, 23:43 UTC

Last modified by the source

10 Sep 2026, 03:51 UTC

Source last checked

26 Oct 2026, 13:45 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-58cw-g322-p94v

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-58cw-g322-p94v

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-44896

Advisory: Mistune has XSS via unescaped figclass/figwidth in Figure directive
IDs: CVE-2026-44896, GHSA-58cw-g322-p94v
Record: https://patchnext.com/advisories/cve-2026-44896 (revision 3, 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 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: mistune 3.2.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI mistune: affected <= 3.2.0; fixed in 3.2.1

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

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## 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-58cw-g322-p94v (OSV record GHSA-58cw-g322-p94v lists affected ranges: PyPI mistune >=0 <3.2.1 (fixed))
- Verified: https://github.com/advisories/GHSA-58cw-g322-p94v (GitHub-reviewed advisory GHSA-58cw-g322-p94v lists affected ranges: PyPI mistune >=0 <=3.2.0)

Commands are suggestions: review each one before running it.