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

CVE-2026-52863 is fixed in unbound on 1 platform, first by DEBIAN-CVE-2026-52863, released July 28, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-52863
- Priority: Routine
- CVSS: 5.9 (Moderate)
- EPSS: 0.0037
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jul 22, 2026
- Weakness: Use After Free
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-52863

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | unbound Debian 13.5 (trixie) | 1.26.1-0+deb13u1 | [DEBIAN-CVE-2026-52863](https://patchblox.com/security/data/fix/linux/debian-cve-2026-52863.md) | Jul 28, 2026 |
| Linux | unbound Debian 14 | 1.25.2-1 | [DEBIAN-CVE-2026-52863](https://patchblox.com/security/data/fix/linux/debian-cve-2026-52863.md) | Jul 28, 2026 |

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Data as of 2026-11-08T00:53:09Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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