Bug 2560075

Summary: CVE-2026-115348 python-mistune: mistune: Denial of Service via unbalanced brackets in 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": ["65d3184d-7393-4094-9ed8-3cdb4592492a"]}
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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: 2559376    

Description Ronit Dey 2026-10-23 17:20:31 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 from 3.0.0 before 3.3.0 contains an algorithmic complexity vulnerability in the inline link parser's parse_link_text function that allows unauthenticated attackers to exhaust CPU with unbalanced brackets. Attackers can submit Markdown containing many unbalanced '[' or '![' characters, forcing repeated unbounded forward scans and tying up worker processes for minutes.
Comment 1 Fedora Update System 2026-10-28 12:00:15 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 02:21:22 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.