CVE-2026-59922

highCVSS 7.5covered by 2 sourcesfirst seen 2026-07-02

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.

CSIRTS triage

product: Mistune Denial of service

What: Quadratic-time parsing can occur on long runs of specific markers.
Who is affected: Users of Mistune plugins/formatting are affected.
Urgency: Remediation is urgent due to the high severity and potential for denial of service.
Action: Update Mistune to the latest version.

AI-assisted analysis generated from the source advisory — verify against the original.

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Exploitation outlook

Low exploitation risk0.37% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 29% of all EPSS-scored CVEs.

Advisory coverage (2)

highCVE-2026-59922: Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, a run of close…nvd · 2026-07-08
highCVE-2026-59922: Mistune plugins/formatting: quadratic-time parsing on long runs of `~~x~~`, `==x==`, and `^^x^…msrc · 2026-07-02

External references

NVD record for CVE-2026-59922

CVE.org record

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