High severity · published Jul 8, 2026
CVE-2026-59925
inline_parser: quadratic-time parsing on long runs of `**x**` and `***x***` emphasis pairs
7.5
CVSS
0.6%
EPSS
No
On KEV
Description
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, long sequences of well-formed double-asterisk or triple-asterisk emphasis pairs around a character cause quadratic work in src/mistune/inline_parser.py because the parser scans forward for matching close markers from every potential opening run, allowing denial of service in default Mistune parsing. This issue is fixed in version 3.3.0.
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)0.6% · higher than 51% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MI
mistune · lepture
< 3.3.0 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-59925
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-59925
Patch
https://github.com/lepture/mistune/commit/5de41fb8e527004dbc363e047a3c380c9288c74f
Release Notes
https://github.com/lepture/mistune/releases/tag/v3.3.0
Exploit
https://github.com/lepture/mistune/security/advisories/GHSA-4j32-57v6-6g45
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