Bug 2507890

Summary: CVE-2026-59928 python-mistune: Mistune: Denial of Service via crafted Markdown document with reference-link definitions [epel-all]
Product: [Fedora] Fedora EPEL Reporter: Hardik Vyas <hvyas>
Component: python-mistuneAssignee: Neil Hanlon <neil>
Status: NEW --- QA Contact: Fedora Extras Quality Assurance <extras-qa>
Severity: medium Docs Contact:
Priority: medium    
Version: epel10CC: epel-packagers-sig, mhroncok, neil, python-packagers-sig, romain.geissler
Target Milestone: ---Keywords: Security, SecurityTracking
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard: {"flaws": ["681b85ed-f463-4aad-a82b-dc1deab01b2c"]}
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Bug Depends On:    
Bug Blocks: 2498156    

Description Hardik Vyas 2026-07-28 07:00:31 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 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.