Mistune: Path Traversal and XSS in Include directive

Exploitation

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

CVSS

not scored

EPSS

• CVE-2026-115355: 0.46% estimated exploitation activity in the next 30 days; percentile 39.98 (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.

The Include directive in src/mistune/directives/include.py does not validate that the resolved file path stays within the source directory, allowing path traversal via ../ sequences to read arbitrary files. Additionally, error messages and included file contents are rendered without HTML escaping, leading to XSS even when escape=True. Affected functions: - Path resolution (lines 27-31) - blockerror() in html.py (line 140) - renderhtmlinclude() (line 72) The Include plugin must be explicitly enabled via the plugins parameter.

Published by the source

23 Oct 2026, 20:46 UTC

Last modified by the source

23 Oct 2026, 21:00 UTC

Source last checked

26 Oct 2026, 13:55 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-h7ww-273w-6cm8

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-h7ww-273w-6cm8

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-h7ww-273w-6cm8

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# Patch Next advisory brief: CVE-2026-115355

Advisory: Mistune: Path Traversal and XSS in Include directive
IDs: CVE-2026-115355, GHSA-h7ww-273w-6cm8
Record: https://patchnext.com/advisories/cve-2026-115355 (revision 3, source checked 26 Oct 2026, 13:55 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Unrated
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: mistune 3.3.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI mistune: affected <= 3.2.0; fixed in 3.3.0

## 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://github.com/advisories/GHSA-h7ww-273w-6cm8 (GitHub-reviewed advisory GHSA-h7ww-273w-6cm8 lists affected ranges: PyPI mistune >=0 <=3.2.0)
- Verified: https://osv.dev/vulnerability/GHSA-h7ww-273w-6cm8 (OSV record GHSA-h7ww-273w-6cm8 lists affected ranges: PyPI mistune >=0 <3.3.0 (fixed))

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