CVE-2026-33079

The record

In versions 3.0.0a1 through 3.2.0 of Mistune, there is a ReDoS (Regular Expression Denial of Service) vulnerability in `LINK_TITLE_RE` that allows an attacker who can supply Markdown for parsing to cause denial of service. The regular expression used for parsing link titles contains overlapping alternatives that can trigger catastrophic backtracking. In both the double-quoted and single-quoted branches, a backslash followed by punctuation can be matched either as an escaped punctuation sequence or as two ordinary characters, creating an ambiguous pattern inside a repeated group. If an attacker supplies Markdown containing repeated ! sequences with no closing quote, the regex engine explores an exponential number of backtracking paths. This is reachable through normal Markdown parsing of inline links and block link reference definitions. A small crafted input can therefore cause significant CPU consumption and make applications using Mistune unresponsive.

Affected packages

Related vulnerabilities

• CVE-2026-49851 Mistune is a Python Markdown parser with renderers and plugins. Also affects python-mistune
• CVE-2026-44897 Mistune is a Python Markdown parser with renderers and plugins. Also affects python-mistune
• CVE-2026-33441 Rejected reason: This CVE is a duplicate of another CVE: CVE-2026-33079. Also affects python-mistune
• CVE-2026-112901 Pillow is a Python imaging library. CWE-1333
• CVE-2026-106454 Twisted is an event-based framework for internet applications, supporting Python 3.6+. CWE-1333
• CVE-2026-77387 geopy is a geocoding library for Python. CWE-1333
• CVE-2026-102990 basic-ftp is an FTP client for Node.js. CWE-1333
• CVE-2026-102473 A flaw was found in dash. CWE-1333