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)
EPSS: 0.002 (8.8th percentile) — read the EPSS interpretation.
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.
Affected products
- Lepture Mistune — versions < 3.2.1
- Mistune_project Mistune
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM, Vendor Advisory)
- security-advisories@github.com (Patch, x_refsource_MISC)
- security-advisories@github.com (x_refsource_MISC, 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.