Medium [CVE-2026-52863] Denial of service due to memory corruption under specific configurations.
This medium-severity Red Hat Linux advisory covers CVE-2026-52863 affecting Red Hat Hardened Images.
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Summary
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.
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.
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. This Moderate flaw in Unbound arises from memory corruption under specific, non-default configurations involving 'respip' or 'rpz' modules, subquery attachment, and 'access-control-view' when the server is under heavy load.
- 1.25.0
- 1.25.1
Official advisory · high-confidence parse· fetched 1 month ago·verify at source
- unbound-main-1.25.2-0.1.hum1
- RHSA-2026:43588
Official advisory · high-confidence parse· fetched 1 month ago·verify at source
Mitigation checklist
- To mitigate this issue, avoid configuring Unbound with a combination of 'respip' or 'rpz' modules, subquery attachment features (such as respip CNAME redirection, dns64, or subnetcache), and 'access-control-view' if these functionalities are not strictly required. Disabling these specific configurations will prevent the conditions under which memory corruption can occur. Any changes to Unbound's configuration will require a service restart to take effect, which may temporarily interrupt DNS resolution services.
Official advisory · high-confidence parse· fetched 1 month ago·verify at source
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