Bug 2567342

Summary:	CVE-2026-121438 python-mistune08: mistune: Denial of Service via deeply nested Markdown brackets [epel-all]
Product:	[Fedora] Fedora EPEL	Reporter:	Oleg Sushchenko <osushche>
Component:	python-mistune08	Assignee:	Orphan Owner <extras-orphan>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	epel10	CC:	epel-packagers-sig, extras-orphan, neil, python-packagers-sig
Target Milestone:	---	Keywords:	Security, SecurityTracking
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:	{"flaws": ["ccfe68c3-afbd-4ba0-b035-d646a7a5b364"]}
Fixed In Version:		Doc Type:	---
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:
Bug Blocks:	2565907

Description Oleg Sushchenko 2026-11-05 15:24:52 UTC

Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.

Mistune before 3.3.3 contains a denial of service vulnerability in InlineParser.parse_link that allows attackers to cause quadratic CPU growth by supplying balanced nested brackets. Attackers can submit crafted Markdown with thousands of nested bracket pairs not forming a valid link, triggering repeated _contains_nested_link scans that exhaust CPU in parsing applications.