Vulnerability Description
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.
CVSS Score
HIGH
Related Weaknesses (CWE)
References
- https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p
- 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
FAQ
What is CVE-2026-49851?
CVE-2026-49851 is a vulnerability with a CVSS score of 7.5 (HIGH). 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...
How severe is CVE-2026-49851?
CVE-2026-49851 has been rated HIGH with a CVSS base score of 7.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-49851?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.