CVE-2026-121437High· 7.5▾ MidnightPoC availableMistune 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…
▾ Midnight zone — Critical, or high with PoC / in-the-wild
impact 41.3 · likelihood 0.1 · exploitation 12
A public proof-of-concept already exists for this vulnerability — see Exploit availability below.
Stakeholder-Specific Vulnerability Categorization from CISA's ADP record at CVE.org: whether exploitation is observed, whether an attack can be automated, and how much of the system is at stake. The CVSS score shown above comes from the assigning CNA record, not NVD.
Exploit-prediction probability, daily snapshots since Nov 5.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via CVEORG
0.6%
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.
mistune >= 3.3.0 < 3.3.4Refer to the linked advisories for vendor-supplied fixes and affected version ranges.
Connected by shared product, vendor, weakness, or advisory.
CVE-2026-115352High· 7.5Mistune before 3.3.0 Quadratic-Time DoS via Unmatched Brackets in Inline Parser
CVE-2026-115347High· 7.5Mistune before 3.3.0 Quadratic Denial of Service via parse_link_text
CVE-2026-121438Medium· 5.3Mistune before 3.3.3 Denial of Service via Balanced Bracket Link Parsing
CVE-2026-115353High· 8.6Mistune before 3.3.0 Path Traversal via include Directive
CVE-2026-115351Medium· 4.7Mistune 3.2.1 before 3.3.0 CSS Injection via Figure Directive figwidth Option
CVE-2026-115354Medium· 6.5Mistune before 3.3.0 Arbitrary Local File Read via Include Directive