Description
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload. This vulnerability is fixed in 3.3.0.
Affected products
Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.
lepture mistune
< 3.3.0affected
References
- https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p ↗
- https://access.redhat.com/security/cve/CVE-2026-49851 ↗
- https://bugzilla.redhat.com/show_bug.cgi?id=2492304 ↗
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-49851.json ↗
- https://access.redhat.com/errata/RHSA-2026:60520 ↗