High 7.5Published Jul 8, 2026

CVE-2026-59928Mistune block_parser: quadratic-time parsing on long lists of repeated reference-link definitions

Updated under an hour ago (Oct 27, 2026, 1:00 PM ET)

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It affects lepture mistune and 1 other product. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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Every CVE for lepture mistune

Exploited in the last 30 days

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, a Markdown document containing many repeated or distinct reference-link definitions causes quadratic work in src/mistune/block_parser.py and the ref_links environment dictionary handling, allowing denial of service through CPU exhaustion. This issue is fixed in version 3.3.0.

CVSS: 7.5 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness (CWE): CWE-407, CWE-1333
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Analyzed
Record last updated: Jul 8, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

lepture mistune lepture:mistune (from the name)	before 3.3.0	CNA record
mistune_project mistune mistune_project:mistune	before 3.3.0	NVD

References

References

https://github.com/lepture/mistune/security/advisories/GHSA-ffq3-xpv3-j92q	x-refsource-confirm, exploit, third-party-advisory
https://github.com/lepture/mistune/commit/2b04d7ba341c16ac78fe82d3076bdd5c3de87c69	x-refsource-misc, patch
https://github.com/lepture/mistune/releases/tag/v3.3.0	x-refsource-misc, release-notes

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.