high7.5
CVE-2026-49851
Mistune: Potential DoS via quadratic-time parsing in parse_link_text
Impact
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.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| pip | mistune | < 3.3.0 | 3.3.0 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-qcq2-496w-v96p
- https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p
- https://nvd.nist.gov/vuln/detail/CVE-2026-49851
- https://access.redhat.com/security/cve/CVE-2026-49851
- https://bugzilla.redhat.com/show_bug.cgi?id=2492304
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-49851.json
- https://access.redhat.com/errata/RHSA-2026:60520