high7.5
CVE-2026-59922
Mistune plugins/formatting: quadratic-time parsing on long runs of `~~x~~`, `==x==`, and `^^x^^` markers (strikethrough / mark / insert)
Impact
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, a run of closed tilde, equals-sign, or caret marker pairs around a character causes quadratic work in src/mistune/plugins/formatting.py when the strikethrough, mark, or insert plugin scans for matching markers from each possible start position, 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-c8j7-8cv4-2xmq
- https://github.com/lepture/mistune/security/advisories/GHSA-c8j7-8cv4-2xmq
- https://nvd.nist.gov/vuln/detail/CVE-2026-59922
- https://github.com/lepture/mistune/commit/96d0f57f8fe9eeb06bb4cff521962a27d7c402e7
- https://github.com/lepture/mistune/releases/tag/v3.3.0
- https://github.com/pypa/advisory-database/tree/main/vulns/mistune/PYSEC-2026-2210.yaml