HIGH 8.7 NVD
CVE-2026-121437
Mistune from 3.3.0 before 3.3.4 contains a denial of service vulnerability that allows remote attackers to exhaust CPU through quadratic-time emphasis delimiter
Mistune from 3.3.0 before 3.3.4 contains a denial of service vulnerability that allows remote attackers to exhaust CPU through quadratic-time emphasis delimiter processing. Attackers can submit small markdown documents with repeated patterns like "*a_b" to trigger an O(n²) index-fixup loop, stalling workers for seconds.
References
- https://github.com/lepture/mistune/commit/b4dd3284e52ec741ed9a227db29ade9017828e90
- https://github.com/lepture/mistune/security/advisories/GHSA-qp42-r9j6-83g9
- https://www.vulncheck.com/advisories/mistune-3.3.0-before-3.3.4-quadratic-time-dos-via-pro
- https://github.com/lepture/mistune/security/advisories/GHSA-qp42-r9j6-83g9
This high severity vulnerability with a CVSS score of 8.7 was published on 2026-11-03 via NVD.
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