Bug 2498156 (CVE-2026-59928)

Summary:	CVE-2026-59928 mistune: Mistune: Denial of Service via crafted Markdown document with reference-link definitions
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	anthomas, ehelms, ggainey, jmitchel, jpasqual, juwatts, kshier, mdellweg, mhulan, nmoumoul, osousa, pcreech, rchan, rjohnson, smallamp, teagle, tmalecek
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in Mistune, a Python Markdown parser. A remote attacker could exploit this vulnerability by providing a specially crafted Markdown document containing numerous repeated or distinct reference-link definitions. This can lead to excessive processing, causing CPU exhaustion and a denial of service (DoS) for the affected system.	Story Points:	---
Clone Of:		Environment:
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Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	2507888, 2507889, 2507890
Bug Blocks:

Description OSIDB Bzimport 2026-07-08 17:02:31 UTC

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.