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Vulnerability · Published Jul 22, 2026 · Assigned by NLnet Labs

CVE-2026-52863Memory corruption could lead to crash and denial of service

Medium 5.9

In plain English

A medium-severity use-after-free in Unbound from NLnet Labs. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 30% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.9Medium
Exploit odds (30 days)0.4%top 69.5% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Alpine:v3.22unbound1.25.2-r0ALPINE-CVE-2026-52863
Alpine:v3.23unbound1.25.2-r0ALPINE-CVE-2026-52863
Alpine:v3.24unbound1.25.2-r0ALPINE-CVE-2026-52863
Debian:12unboundno fix listedDEBIAN-CVE-2026-52863
Debian:13unbound1.26.1-0+deb13u1DEBIAN-CVE-2026-52863
Debian:14unbound1.25.2-1DEBIAN-CVE-2026-52863
Ubuntu:22.04:LTSunboundno fix listedUBUNTU-CVE-2026-52863
Ubuntu:24.04:LTSunboundno fix listedUBUNTU-CVE-2026-52863
Ubuntu:26.04:LTSunboundno fix listedUBUNTU-CVE-2026-52863
Ubuntu:26.10unboundno fix listedUBUNTU-CVE-2026-52863

Affected products (as reported)

VendorProductVersions
NLnet Labs Unbound 1.25.0 – before 1.25.2

Weakness: CWE-416 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

References