CVE-2026-59922: 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 i

highCVSS 7.5CVE-2026-59922

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.

Details

Source: NVD Recent CVEs (US · database · site)
Severity: high — CVSS 7.5
Published: 2026-07-08
Last updated: 2026-07-09
Exploitation: Not in CISA KEV at last sync

Original advisory: https://nvd.nist.gov/vuln/detail/CVE-2026-59922

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-599220.37% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 29% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-59922	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

highCVE-2026-59922: Mistune plugins/formatting: quadratic-time parsing on long runs of `~~x~~`, `==x==`, and `^^x^…msrc

Recent advisories for Mistune is a

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

highGHSA-qcq2-496w-v96p: Mistune: Potential DoS via quadratic-time parsing in parse_link_textghsa · 2026-07-09
mediumCVE-2026-59930: Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the toc plugin…nvd · 2026-07-08
mediumCVE-2026-59929: Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the safe_url f…nvd · 2026-07-08
highCVE-2026-59928: Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, a Markdown doc…nvd · 2026-07-08
mediumCVE-2026-59927: Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the Include di…nvd · 2026-07-08
mediumCVE-2026-59926: Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, render_admonit…nvd · 2026-07-08