[ CVE-2026-121438 · Published 3 Nov 2026 ]
Vulnerability in lepture mistune
CVSS 5.3
EPSS <1%No fix listed yet
[ Description ]Official description
Mistune before 3.3.3 contains a denial of service vulnerability in InlineParser.parse_link that allows attackers to cause quadratic CPU growth by supplying balanced nested brackets. Attackers can submit crafted Markdown with thousands of nested bracket pairs not forming a valid link, triggering repeated _contains_nested_link scans that exhaust CPU in parsing applications.
[ Fixes ]Fixes and patches
No fix or interim patch is linked from our sources yet. Check the vendor references below and limit exposure of affected systems until a fix is available.