Bug 2506141 (CVE-2026-52863)

Summary: CVE-2026-52863 unbound: Unbound: Denial of service due to memory corruption under specific configurations.
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, 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, a validating, recursive, and caching Domain Name System (DNS) resolver. When configured with specific modules and under heavy load, a memory corruption vulnerability can occur due to improper handling of view names during subquery processing. This issue could lead to a denial of service (DoS) by causing the Unbound server to crash.
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Bug Depends On: 2509271    
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Description OSIDB Bzimport 2026-07-22 14:02:19 UTC 
In NLnet Labs Unbound 1.25.0 up to and including 1.25.1, a fix that makes the 'respip' and 'dns64' modules work together, creates a shallow copy of the view name in effect that could lead to memory corruption if the owner of the original view name is jostled out when Unbound is under pressure. Unbound needs to be configured with one of 'respip'/'rpz' modules, together with a module that can attach subqueries (respip CNAME redirection, dns64, subnetcache) and a configured 'access-control-view' while Unbound is under pressure so that joslte logic kicks in and starts dropping slow queries. The subquery is getting a shallow copy of the view name and if the super query which owns the view name is jostled out, memory corruption can occur. Likelihood of a crash is low, since it relies heavily on the underlying memory allocator and the memory layout. Debug memory builds (e.g., ASAN) that catch the free terminate the server.