GHSA-c8j7-8cv4-2xmq: mistune (CVE-2026-59922)

Package	Ecosystem	Affected	Fixed in
mistune	PyPI	<3.3.0	3.3.0

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

Mistune versions before 3.3.0 are vulnerable to a denial of service in the strikethrough, mark, and insert formatting plugins. Parsing a long run of paired markers such as double tildes, equals signs, or carets takes quadratic time, so an attacker who can submit text for parsing can tie up the process with a crafted input. Upgrade mistune to version 3.3.0 or later. The source gives few details beyond this.

Written 5 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

Score	Rating	CVSS	Vector	Source
7.5	High	3.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H	CNA (GitHub_M)

CISA KEV Not listed.
EPSS 0.0064, the 51st percentile, on 15 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

31 Oct 2026, 14:42 UTC First seen by agentprime
31 Oct 2026, 14:42 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.