CVE-2026-121437

EUVD-2026-115859
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.
ProviderTypeBase ScoreAtk. VectorAtk. ComplexityPriv. RequiredVector
NISTPrimary
7.5 HIGH
NETWORK
LOW
NONE
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Awaiting analysis
This vulnerability is currently awaiting analysis.
Base Score
CVSS 3.x
EPSS Score
Percentile: Unknown
Common Weakness Enumeration
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-process-emphasis-delimiters
https://github.com/lepture/mistune/security/advisories/GHSA-qp42-r9j6-83g9