CVE-2026-33079: Lepture Mistune

High severity, CVSS 7.5. EPSS: 0.7% chance of exploitation in the next 30 days.

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 products

• Lepture Mistune: from 3.0.0a1, up to and including 3.2.0
• Red Hat Red Hat Migration Toolkit For Applications 8.2: before 1784109883 (fixed in 1784109883)
• Red Hat Red Hat Openshift Ai 3.4: before 1787073866 (fixed in 1787073866); before 1787073936 (fixed in 1787073936); before 1787073873 (fixed in 1787073873); before 1787073459 (fixed in 1787073459); before 1787073611 (fixed in 1787073611); before 1787073451 (fixed in 1787073451); …
• Red Hat Red Hat Openshift Ai Rhoai
• Red Hat Red Hat Satellite 6

Published 2026-05-06. Last modified 2026-08-28.