CVE-2026-49851

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload. This vulnerability is fixed in 3.3.0.

• CWE-400
• CWE-407
• CWE-770
• CWE-1333

• https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p
• https://access.redhat.com/errata/RHSA-2026:60520
• https://access.redhat.com/security/cve/CVE-2026-49851
• https://bugzilla.redhat.com/show_bug.cgi?id=2492304
• https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-49851.json

Published

Jun 24, 2026

Last Modified

Aug 28, 2026

Status

Deferred

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
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