High severity · published Oct 22, 2026
CVE-2026-115349
Mistune 3.0.0 before 3.3.0 Denial of Service via Nested Bracket Parsing
New
7.5
CVSS
0.3%
EPSS
No
On KEV
Description
Mistune from 3.0.0 before 3.3.0 contains an algorithmic complexity denial of service vulnerability in the parse_link_text function in src/mistune/helpers.py. Attackers can submit markdown with deeply nested square brackets triggering quadratic parsing time, exhausting server CPU with small crafted requests.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 28% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MI
mistune · lepture
3.0.0 before 3.3.0 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-115349
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-115349
github.com
https://github.com/lepture/mistune/security/advisories/GHSA-3q64-rw38-243v
www.vulncheck.com
https://www.vulncheck.com/advisories/mistune-3.0.0-before-3.3.0-denial-of-service-via-nested-bracket-parsing
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