High 8.7Published Jun 24, 2026

CVE-2026-49851Mistune: Potential DoS via quadratic-time parsing in parse_link_text

Updated under an hour ago (Oct 28, 2026, 1:20 AM ET)

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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, Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload. This vulnerability is fixed in 3.3.0.

CVSS: 8.7 HIGH (v4.0, CNA)CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Weakness (CWE): CWE-400, CWE-770, 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: Deferred
Record last updated: Aug 28, 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
Red Hat Red Hat OpenShift AI 3.4 redhat:openshift_ai	from 1787073866 not affected	CISA ADP
Red Hat Migration Toolkit for Applications 8 redhat:migration_toolkit_applications	8	CISA ADP
Red Hat Red Hat OpenShift Container Platform 4 redhat:openshift	4	CISA ADP
Red Hat Red Hat Satellite 6 redhat:satellite	6	CISA ADP

References

References

https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p	x-refsource-confirm
https://access.redhat.com/errata/RHSA-2026:60520
https://access.redhat.com/security/cve/CVE-2026-49851
https://bugzilla.redhat.com/show_bug.cgi?id=2492304
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-49851.json

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.