Medium severity · published Jul 8, 2026
CVE-2026-59926
Mistune: XSS via unescaped class option in Admonition directive
6.1
CVSS
0.3%
EPSS
No
On KEV
Description
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Confidentiality
Low
Integrity
Low
Availability
None
Scope
Changed
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 26% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MI
mistune · lepture
< 3.2.1 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-59926
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-59926
Patch
https://github.com/lepture/mistune/commit/a3cb6e5655308797e8be021d6c7b5bab13cbace2
Release Notes
https://github.com/lepture/mistune/releases/tag/v3.2.1
Vendor Advisory
https://github.com/lepture/mistune/security/advisories/GHSA-g97x-gvcm-x72h
More from mistune
8.6
CVE-2026-115353
Mistune before 3.3.0 Path Traversal via include Directive
7.5
CVE-2026-115355
Mistune before 3.3.0 Path Traversal and XSS via Include Directive
7.5
CVE-2026-115352
Mistune before 3.3.0 Quadratic-Time DoS via Unmatched Brackets in Inline Parser
7.5
CVE-2026-115349
Mistune 3.0.0 before 3.3.0 Denial of Service via Nested Bracket Parsing
7.5
CVE-2026-115348
Mistune before 3.3.0 Quadratic-Time DoS via parse_link_text