What is CVE-2026-59930?

CVE-2026-59930 is a medium-severity vulnerability in Lepture Mistune, classified under Insufficient Verification of Data Authenticity. CVSS score: 4.3/10. Published 2026-07-08.

How severe is CVE-2026-59930?

Medium severity. CVSS v3 base score is 4.3 out of 10.

Vulnerability in Lepture Mistune

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.

Published 2026-07-08 · last modified 2026-07-09.

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N.

EPSS exploit prediction

EPSS: 0.002 (8.1th percentile), scored 2026-10-08.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 8th percentile — 8.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: 0.000

Affected products

Lepture Mistune — versions < 3.3.0
Mistune Project

Weakness classification (CWE)

References

github.com/lepture/mistune/security/advisories/GHSA-2hm2-hc3v-44h9 (Exploit, Third Party Advisory)
github.com/lepture/mistune/commit/c4093c4742ed0d10d9332fb8edb455869b7b581b (Patch)
github.com/lepture/mistune/releases/tag/v3.3.0 (Release Notes)

Frequently asked questions

What is CVE-2026-59930?: CVE-2026-59930 is a medium-severity vulnerability in Lepture Mistune, classified under Insufficient Verification of Data Authenticity. CVSS score: 4.3/10. Published 2026-07-08.
How severe is CVE-2026-59930?: Medium severity. CVSS v3 base score is 4.3 out of 10.