{"id":"CVE-2026-121437","title":"Mistune 3.3.0 before 3.3.4 Quadratic-Time DoS via _process_emphasis_delimiters","summary":"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 patt…","severity":"high","cvss":7.5,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","cvssSource":"cna","cwe":["CWE-407"],"vendor":"lepture","product":"mistune","affected":["mistune >= 3.3.0 < 3.3.4"],"ssvc":{"exploitation":"poc","automatable":"no","technicalImpact":"partial","timestamp":"2026-11-03T16:58:25.525426Z"},"exploitAvailable":true,"published":"2026-11-03","updated":"2026-11-03","sourceUpdated":"2026-11-03T16:59:17.405Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-121437","references":[{"url":"https://github.com/lepture/mistune/security/advisories/GHSA-qp42-r9j6-83g9","label":"GitHub Security Advisory (GHSA-qp42-r9j6-83g9)"},{"url":"https://github.com/lepture/mistune/commit/b4dd3284e52ec741ed9a227db29ade9017828e90","label":"Patch Commit"},{"url":"https://www.vulncheck.com/advisories/mistune-3.3.0-before-3.3.4-quadratic-time-dos-via-process-emphasis-delimiters","label":"VulnCheck Advisory: Mistune 3.3.0 before 3.3.4 Quadratic-Time DoS via _process_emphasis_delimiters"}],"tags":["cve.org","exploit-available"],"epss":0.00619,"epssPercentile":0.49909,"ingestedAt":"2026-11-05T20:33:06.294Z","slug":"CVE-2026-121437","body":"## Overview\n\nMistune 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.\n\n## Affected\n\n- `mistune >= 3.3.0 < 3.3.4`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"midnight","depthScore":53,"depthScoreParts":{"impact":41.3,"likelihood":0.1,"exploitation":12,"ransomware":0},"changes":[]}