Bug 2565894 (CVE-2026-121437)

Summary: CVE-2026-121437 mistune: mistune: Denial of Service via quadratic-time emphasis delimiter processing
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, sghai, sidsharm, suppawar, vlaad
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in mistune. A remote attacker could cause a Denial of Service (DoS) by submitting specially crafted Markdown documents containing repeating emphasis delimiter patterns. Processing these patterns triggers an inefficient index-fixup loop that consumes excessive CPU resources and stalls application workers.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 2568135, 2568136, 2568137    
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Description OSIDB Bzimport 2026-11-03 15:40:35 UTC
Mistune from 3.3.0 before 3.3.4 contains a denial of service vulnerability that allows remote attackers to exhaust CPU through quadratic-time emphasis delimiter processing. Attackers can submit small markdown documents with repeated patterns like "*a_b" to trigger an O(n²) index-fixup loop, stalling workers for seconds.