Vulnerability · Published Jul 8, 2026 · Assigned by GitHub_M
CVE-2026-59925inline_parser: quadratic-time parsing on long runs of `**x**` and `***x***` emphasis pairs
High 7.5
In plain English
A high-severity regular-expression denial of service in mistune from lepture. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 51% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:13 | mistune | no fix listed | DEBIAN-CVE-2026-59925 |
| Debian:14 | mistune | no fix listed | DEBIAN-CVE-2026-59925 |
| PyPI | mistune | 3.3.0 | GHSA-4j32-57v6-6g45 |
| PyPI | mistune | 3.3.0 | PYSEC-2026-2213 |
| Ubuntu:22.04:LTS | mistune | no fix listed | UBUNTU-CVE-2026-59925 |
| Ubuntu:24.04:LTS | mistune | no fix listed | UBUNTU-CVE-2026-59925 |
| Ubuntu:25.10 | mistune | no fix listed | UBUNTU-CVE-2026-59925 |
| Ubuntu:26.04:LTS | mistune | no fix listed | UBUNTU-CVE-2026-59925 |
| Ubuntu:26.10 | mistune | no fix listed | UBUNTU-CVE-2026-59925 |
Affected products (as reported)
Weakness: CWE-407, CWE-1333 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
References
- https://github.com/lepture/mistune/security/advisories/GHSA-4j32-57v6-6g45 x_refsource_CONFIRM
- https://github.com/lepture/mistune/commit/5de41fb8e527004dbc363e047a3c380c9288c74f x_refsource_MISC
- https://github.com/lepture/mistune/releases/tag/v3.3.0 x_refsource_MISC