high7.5
CVE-2026-59928
Mistune block_parser: quadratic-time parsing on long lists of repeated reference-link definitions
Impact
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, a Markdown document containing many repeated or distinct reference-link definitions causes quadratic work in src/mistune/block_parser.py and the ref_links environment dictionary handling, allowing denial of service through CPU exhaustion. This issue is fixed in version 3.3.0.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| pip | mistune | < 3.3.0 | 3.3.0 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Mistune Project | Mistune | before 3.3.0 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-ffq3-xpv3-j92q
- https://github.com/lepture/mistune/security/advisories/GHSA-ffq3-xpv3-j92q
- https://nvd.nist.gov/vuln/detail/CVE-2026-59928
- https://github.com/lepture/mistune/commit/2b04d7ba341c16ac78fe82d3076bdd5c3de87c69
- https://github.com/lepture/mistune/releases/tag/v3.3.0
- https://github.com/pypa/advisory-database/tree/main/vulns/mistune/PYSEC-2026-2216.yaml