# CVE-2026-59927: lepture Mistune uncontrolled recursion in Include directive

Source: https://junglewise.ai/threats/cve-2026-59927-lepture-mistune-uncontrolled-recursion-in-include-directive  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-08. Updated: 2026-07-20  
License: CC BY 4.0 with a link back

CVE-2026-59927 · Severity: medium · CVSS 5.3 · Published 2026-07-08

Mistune is a Python library used to convert Markdown text into HTML. A vulnerability in its 'include' feature allows an attacker to provide specially crafted files that reference each other in a loop. When the library tries to process these files, it enters an infinite loop that crashes the application, leading to a denial of service.

Technologies: [mistune (PyPI)](https://junglewise.ai/threats/technologies/mistune). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-59927 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-59927 being exploited in the wild.

**How severe is CVE-2026-59927?** Medium severity, with a CVSS score of 5.3, published 8 July 2026.

**Which products and versions are affected?** mistune (PyPI) < 3.3.0, ECOSYSTEM:introduced=0,fixed=3.3.0.

**Is there a fix for CVE-2026-59927?** Yes. mistune (PyPI): upgrade to 3.3.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-59927 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-59927?** Check whether you run mistune (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- mistune (PyPI): upgrade to 3.3.0 or later

  ```sh
  pip install "mistune>=3.3.0"
  ```


## Technical details

The 'Include' directive in Mistune's RSTDirective plugin fails to properly detect transitive inclusion cycles. While it prevents a file from including itself directly, it does not track the stack of included files during recursive parsing. An attacker with the ability to provide Markdown files (e.g., in a CMS or documentation platform) can create a cycle where 'a.md' includes 'b.md' and 'b.md' includes 'a.md'. This causes the Python interpreter to exceed its maximum recursion depth, raising a 'RecursionError' that propagates and crashes the calling process. The vulnerability is fixed in version 3.3.0 by implementing an include stack to track and reject cyclic references.

## Affected products

- lepture mistune < 3.3.0

## Identifiers

- CVE-2026-59927
- GHSA-8mpj-m6qm-5qr8
- PYSEC-2026-2215

## Timeline

- 2026-06-21: disclosed
- 2026-07-20: advisory
- 2026-07-20: patched: Fixed in version 3.3.0

## References

- [https://github.com/lepture/mistune/security/advisories/GHSA-8mpj-m6qm-5qr8](https://github.com/lepture/mistune/security/advisories/GHSA-8mpj-m6qm-5qr8)
- [https://github.com/lepture/mistune/commit/1bef343ade163fc3bb95572b15be720084cdb993](https://github.com/lepture/mistune/commit/1bef343ade163fc3bb95572b15be720084cdb993)
- [https://github.com/lepture/mistune/releases/tag/v3.3.0](https://github.com/lepture/mistune/releases/tag/v3.3.0)
- [https://github.com/pypa/advisory-database/tree/main/vulns/mistune/PYSEC-2026-2215.yaml](https://github.com/pypa/advisory-database/tree/main/vulns/mistune/PYSEC-2026-2215.yaml)
- [https://api.github.com/repos/lepture/mistune/security-advisories/GHSA-8mpj-m6qm-5qr8](https://api.github.com/repos/lepture/mistune/security-advisories/GHSA-8mpj-m6qm-5qr8)

## Related threats

- [Mistune path traversal and XSS in Include directive](https://junglewise.ai/threats/duplicate-advisory-mistune-path-traversal-and-xss-in-include-directive-bf25c187)
- [Mistune path traversal and XSS in Include directive](https://junglewise.ai/threats/cve-2026-115355-mistune-before-3-3-0-contains-a-path-traversal-vulnerability-in)
- [Mistune uncontrolled recursion in HTML rendering](https://junglewise.ai/threats/cve-2026-76098-mistune-uncontrolled-recursion-in-html-rendering)
- [lepture Mistune predictable ID generation in TOC plugin](https://junglewise.ai/threats/cve-2026-59930-lepture-mistune-predictable-id-generation-in-toc-plugin)
- [lepture mistune XSS via incomplete URL scheme filtering in HTML renderer](https://junglewise.ai/threats/cve-2026-59929-lepture-mistune-xss-via-incomplete-url-scheme-filtering-in-html)