# CVE-2026-52863: NLnet Labs Unbound use-after-free in respip and dns64 modules

Source: https://junglewise.ai/threats/cve-2026-52863-nlnet-labs-unbound-use-after-free-in-respip-and-dns64-modules  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-22. Updated: 2026-07-22  
License: CC BY 4.0 with a link back

CVE-2026-52863 · Severity: medium · CVSS 5.9 · Published 2026-07-22

NLnet Labs Unbound is a widely used DNS resolver that translates human-readable domain names into IP addresses. A memory management flaw in certain configurations could allow a remote attacker to cause the service to crash or behave unpredictably when the server is under heavy load. This could lead to a denial-of-service, impacting the ability of users and applications to access internet resources.

Technologies: [NLnet Labs Unbound](https://junglewise.ai/threats/technologies/unbound). Vendors: [NLnet Labs](https://junglewise.ai/threats/vendors/nlnet-labs).

## Quick answers

**Is CVE-2026-52863 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-52863 being exploited in the wild.

**How severe is CVE-2026-52863?** Medium severity, with a CVSS score of 5.9, published 22 July 2026.

**Which products and versions are affected?** NLnet Labs Unbound 1.25.0 to 1.25.1.

**Is there a fix for CVE-2026-52863?** A patch was published on 2026-07-22: Fixed in version 1.25.2 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-52863 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-52863?** Check whether you run NLnet Labs Unbound at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A use-after-free vulnerability (CWE-416) exists in Unbound versions 1.25.0 through 1.25.1 due to the creation of a shallow copy of a 'view name' when the 'respip' and 'dns64' modules interact. The vulnerability is triggered when Unbound is configured with 'respip' or 'rpz' modules alongside subquery-attaching modules (like dns64 or subnetcache) and 'access-control-view'. Under high load, Unbound's 'jostle' logic may drop a super query that owns the original view name, leaving the subquery with a dangling pointer. This leads to memory corruption or a server crash, particularly in builds with memory protections like ASAN. The issue is resolved in version 1.25.2.

## Affected products

- NLnet Labs Unbound 1.25.0 to 1.25.1

## Timeline

- 2026-07-22: disclosed
- 2026-07-22: advisory
- 2026-07-22: patched: Fixed in version 1.25.2

## References

- [https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-52863.txt](https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-52863.txt)

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