Bug 2535054 (CVE-2026-81634)

Summary: CVE-2026-81634 unbound: Unbound: Heap buffer overflow via malicious DNSSEC response
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Unbound. This vulnerability allows a remote attacker to cause a heap buffer overflow during the processing of DNSSEC responses. By sending a specially crafted DNSSEC response, a malicious server or an attacker tampering with network traffic can trigger this flaw. This could lead to a denial of service, making the Unbound service unavailable.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 2536900    
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Description OSIDB Bzimport 2026-09-16 09:04:41 UTC 
In NLnet Labs Unbound up to and including 1.26.0, a 255 length query name with a large TCP response can lead to a heap buffer overflow during the RRSet canonicalisation routine. This is caused by missing to add the first owner name into the buffer length check. A malicious actor operating a malicious name server or tampering with an incoming response to Unbound (canonicalisation happens before DNSSEC validation), can trigger the vulnerability.