CVE-2026-59927: mistune — Exploit & Fix

Description

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the Include directive in src/mistune/directives/include.py detects only direct self-includes and not indirect cycles, allowing two markdown files that include each other to trigger unbounded recursion, raise RecursionError, and crash the rendering request. This issue is fixed in version 3.3.0.

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CVSS v3.1 Score

5.3

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS — Exploit Prediction

0.0031

Probability of exploitation

0.23%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-674 CWE-674

CWE-755 CWE-755

Affected Products

Vendor	Product	Versions
mistune_project	mistune	< 3.3.0

References

Advisories & Patches

https://github.com/lepture/mistune/commit/1bef343ade163fc3bb95572b15be720084cdb993

Exploits

https://github.com/lepture/mistune/security/advisories/GHSA-8mpj-m6qm-5qr8

Other References

https://github.com/lepture/mistune/releases/tag/v3.3.0

Frequently Asked Questions

What is CVE-2026-59927? +

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the Include directive in src/mistune/directives/include.py detects only direct self-includes and not indirect cycles, allowing two markdown files that include each other to trigger unbounded recursion, raise RecursionError, and crash the rendering request. This issue is fixed in version 3.3.0. It has a CVSS v3.1 base score of 5.3 (MEDIUM).

How severe is CVE-2026-59927? +

CVE-2026-59927 has a CVSS v3.1 score of 5.3 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0031, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-59927? +

CVE-2026-59927 affects products from mistune_project, specifically: mistune. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-59927? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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