Bug 2560121

Summary: CVE-2026-115352 python-mistune: mistune: Denial of Service via unmatched brackets in inline link parser [fedora-43]
Product: [Fedora] Fedora Reporter: Ronit Dey <rdey>
Component: python-mistuneAssignee: Miro Hrončok <mhroncok>
Status: ON_QA --- QA Contact: Fedora Extras Quality Assurance <extras-qa>
Severity: high Docs Contact:
Priority: high    
Version: 43CC: epel-packagers-sig, mhroncok, neil, python-packagers-sig, romain.geissler
Target Milestone: ---Keywords: Security, SecurityTracking
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Hardware: Unspecified   
OS: Unspecified   
Whiteboard: {"flaws": ["82d2fe82-d537-4b89-98b5-bf5033c012b8"]}
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On:    
Bug Blocks: 2559293    

Description Ronit Dey 2026-10-23 17:44:00 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 3.3.0 contains an algorithmic complexity vulnerability in the inline link parser that allows unauthenticated attackers to exhaust CPU by submitting long runs of unmatched '[' characters. Attackers can send small markdown payloads that trigger O(N^2) parse_link_text and parse_link_label probing, occupying rendering workers for 30+ seconds per 16 KB input.
Comment 1 Fedora Update System 2026-10-28 12:00:24 UTC 
FEDORA-2026-340793a2f1 (python-mistune-3.3.4-1.fc43) has been submitted as an update to Fedora 43.
https://bodhi.fedoraproject.org/updates/FEDORA-2026-340793a2f1
Comment 2 Fedora Update System 2026-10-29 02:21:30 UTC 
FEDORA-2026-340793a2f1 has been pushed to the Fedora 43 testing repository.
Soon you'll be able to install the update with the following command:
`sudo dnf upgrade --enablerepo=updates-testing --refresh --advisory=FEDORA-2026-340793a2f1`
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2026-340793a2f1

See also https://fedoraproject.org/wiki/QA:Updates_Testing for more information on how to test updates.