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Advisory record · GHSA-6m44-fpc8-c3rq

Mistune: Denial of Service — RecursionError via Excessive Emphasis Markers in Markdown

CVSS 7.5 HighEPSS 0.0049 · 42nd percentile

Published by the GitHub Advisory Database at 2 Sept 2026, 15:14 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
mistunePyPI>=3.3.0, <3.3.33.3.3
Identifiers
GHSA-6m44-fpc8-c3rq · CVE-2026-76098 · PYSEC-2026-3863
Weakness (CWE)
CWE-674
Tags
Published
2 Sept 2026
Updated
10 Sept 2026

Machine-written summary

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

Mistune versions 3.3.0 before 3.3.3 are vulnerable to a denial of service caused by deeply nested emphasis markers. An attacker who can submit Markdown to an application using mistune can send a few thousand consecutive asterisk characters, causing the Python process to crash with a RecursionError. Upgrade to mistune 3.3.3 or later, which contains the fix. The source gives no workaround beyond that.

Written 1 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

ScoreRatingCVSSVectorSource
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 0.0049, the 42nd percentile, on 14 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 14:10 UTC First seen by agentprime
  2. 31 Oct 2026, 14:10 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.