CVE-2026-59925

inline_parser: quadratic-time parsing on long runs of `**x**` and `***x***` emphasis pairs

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.

Affected

lepture · mistune

CVSS v3.1 GITHUB

7.5 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

0.64% chance of exploitation in the next 30 days, 50th percentile

Published

2026-07-08

Proof-of-concept exploits (1)

• advisories/GHSA-4j32-57v6-6g45

Security advisories

• lepture/mistune/security/advisories/GHSA-4j32-57v6-6g45
• lepture/mistune/commit/5de41fb8e527004dbc363e047a3c380c9288c74f

References

• CVE Record
• NVD entry