CVE-2026-121438Medium· 5.3▾ TwilightPoC availableMistune before 3.3.3 contains a denial of service vulnerability in InlineParser.parse_link that allows attackers to cause quadratic CPU growth by supplying balanced nested brackets. Attackers can submit crafted Markdown with thousands of…
▾ Twilight zone — High severity, or a signal on a lesser flaw
impact 29.2 · 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
0.3%
Last analysed / modified upstream
Exploit / PoC code exists
Mistune before 3.3.3 contains a denial of service vulnerability in InlineParser.parse_link that allows attackers to cause quadratic CPU growth by supplying balanced nested brackets. Attackers can submit crafted Markdown with thousands of nested bracket pairs not forming a valid link, triggering repeated _contains_nested_link scans that exhaust CPU in parsing applications.
mistune < 3.3.3Refer to the linked advisories for vendor-supplied fixes and affected version ranges.
Field changes observed since this record was first indexed.
Connected by shared product, vendor, weakness, or advisory.
CVE-2026-115348High· 7.5Mistune before 3.3.0 Quadratic-Time DoS via parse_link_text
CVE-2026-121437High· 7.5Mistune 3.3.0 before 3.3.4 Quadratic-Time DoS via _process_emphasis_delimiters
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
CVE-2026-49851High· 7.5Mistune: Potential DoS via quadratic-time parsing in parse_link_text