What is CVE-2026-59926?

CVE-2026-59926 is a medium-severity vulnerability in Lepture Mistune, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2026-07-08.

How severe is CVE-2026-59926?

Medium severity. CVSS v3 base score is 6.1 out of 10.

XSS in Lepture Mistune

CVE-2026-59926

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, render_admonition() in src/mistune/directives/admonition.py concatenates the Admonition directive :class: option into the HTML class attribute without escaping, allowing attribute injection and cross-site scripting even when HTMLRenderer escape mode is enabled. This issue is fixed in version 3.2.1.

Vulnerability class: XSS (Cross-Site Scripting)

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

CVSS v3 metric

CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.003 (23.7th percentile), scored 2026-10-09.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 24th percentile — 23.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: 0.000

Affected products

Lepture Mistune — versions < 3.2.1
Mistune Project

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

github.com/lepture/mistune/security/advisories/GHSA-g97x-gvcm-x72h (Vendor Advisory)
github.com/lepture/mistune/commit/a3cb6e5655308797e8be021d6c7b5bab13cbace2 (Patch)
github.com/lepture/mistune/releases/tag/v3.2.1 (Release Notes)

Frequently asked questions

What is CVE-2026-59926?: CVE-2026-59926 is a medium-severity vulnerability in Lepture Mistune, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2026-07-08.
How severe is CVE-2026-59926?: Medium severity. CVSS v3 base score is 6.1 out of 10.