CVE-2026-59930: mistune — Exploit & Fix

Description

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the toc plugin and TableOfContents directive generate heading IDs as predictable toc_N values without slugifying the heading text, allowing attacker-controlled id="toc_N" content to collide with generated anchors and redirect same-page navigation, CSS selectors, or JavaScript handlers. This issue is fixed in version 3.3.0.

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CVSS v3.1 Score

4.3

MEDIUM

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

EPSS — Exploit Prediction

0.0013

Probability of exploitation

0.03%

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-345 CWE-345

CWE-1284 CWE-1284

Affected Products

Vendor	Product	Versions
mistune_project	mistune	< 3.3.0

References

Advisories & Patches

https://github.com/lepture/mistune/commit/c4093c4742ed0d10d9332fb8edb455869b7b581b

Exploits

https://github.com/lepture/mistune/security/advisories/GHSA-2hm2-hc3v-44h9 https://github.com/lepture/mistune/security/advisories/GHSA-2hm2-hc3v-44h9

Other References

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

Frequently Asked Questions

What is CVE-2026-59930? +

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the toc plugin and TableOfContents directive generate heading IDs as predictable toc_N values without slugifying the heading text, allowing attacker-controlled id="toc_N" content to collide with generated anchors and redirect same-page navigation, CSS selectors, or JavaScript handlers. This issue is fixed in version 3.3.0. It has a CVSS v3.1 base score of 4.3 (MEDIUM).

How severe is CVE-2026-59930? +

CVE-2026-59930 has a CVSS v3.1 score of 4.3 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0013, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-59930? +

CVE-2026-59930 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-2026-59930? +

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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