high Patched

Mistune: Path Traversal and XSS in Include directive

CVE-2026-115355 · GHSA-h7ww-273w-6cm8 · published 23 Oct 2026

How serious is it

  • Severity: high.
  • No exploit prediction (EPSS) score yet.
  • Not on the CISA list of exploited vulnerabilities.
  • No public exploit in Exploit-DB.

Is your app affected by CVE-2026-115355?

Paste this prompt into Claude Code, Cursor or any AI coding tool: it runs a free Shippable scan of your project and fixes what it finds. Built with Lovable, Bolt or v0? Scan your live app. Or upload your package file.

Who is affected

  • mistune (PyPI) <= 3.2.0

How to check

  1. Run pip show mistune in your project to see the installed version, including copies pulled in by other packages.
  2. Or paste your lockfile into the checker: it lists every package with a known vulnerability, this one included.
  3. Or run npx shippable-dev scan localhost:3000 in your project folder. It reads your lockfile and flags this vulnerability along with every other known one.

How to fix

Copies a prompt for Claude Code, Cursor or Codex: it checks your lockfiles for this and upgrades it.
  1. Upgrade mistune to 3.3.0 or later, commit the lockfile and redeploy.
  2. If a vulnerable version was live, check your logs and rotate the secrets that server could read.

The advisory

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) - `block_error()` in html.py (line 140) - `render_html_include()` (line 72) The Include plugin must be explicitly enabled via the plugins parameter.

Check your whole app

Dependencies are only half of it. Free and read-only: before you push, run npx shippable-dev scan localhost:3000 in your project folder, no account needed. For your live app, you prove it's yours with a one-line tag first.

References

Merged from GitHub Advisory Database, OSV. Last updated 26 Oct 2026. All vulnerabilities · RSS · JSON

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