CVE-2026-49851
Mistune: Potential DoS via quadratic-time parsing in parse_link_text
CVSS Score
7.5
EPSS Score
0.0%
EPSS Percentile
0th
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 | CWE-400 CWE-770 CWE-407 |
| Vendor | lepture |
| Product | mistune |
| Published | Jun 24, 2026 |
| Last Updated | Jul 15, 2026 |
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Affected Versions
lepture / mistune
< 3.3.0
References
github.com: https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p access.redhat.com: https://access.redhat.com/security/cve/CVE-2026-49851 bugzilla.redhat.com: https://bugzilla.redhat.com/show_bug.cgi?id=2492304 security.access.redhat.com: https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-49851.json