What’s Vulnerable › Vulnerabilities

CVE-2026-59925: inline_parser: quadratic-time parsing on long runs of `**x**` and `***x***` emphasis pairs

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-07-08 · updated 2026-10-25
• Weakness: CWE-407

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.

Affected products

• lepture mistune: before 3.3.0 — fixed in 3.3.0

How to fix

Upgrade to a fixed version: lepture mistune 3.3.0. Check the vendor advisory for mitigations.

References

• https://github.com/lepture/mistune/commit/5de41fb8e527004dbc363e047a3c380c9288c74f
• https://github.com/lepture/mistune/releases/tag/v3.3.0
• https://github.com/lepture/mistune/security/advisories/GHSA-4j32-57v6-6g45

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