# CVE-2026-50046: NLnet Labs Unbound use-after-free in DNS-over-TLS forwarding

Source: https://junglewise.ai/threats/cve-2026-50046-nlnet-labs-unbound-use-after-free-in-dns-over-tls-forwarding  
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-2026-50046 · Severity: medium · CVSS 5.9 · Published 2026-07-22

Unbound is a widely used DNS resolver that helps translate human-readable domain names into IP addresses. A vulnerability in how it handles secure DNS-over-TLS connections can allow an attacker to crash the service by sending specific queries under high-load conditions. This results in a denial of service, preventing users and systems from resolving domain names and potentially disrupting internet connectivity for the affected network.

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

## Quick answers

**Is CVE-2026-50046 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-50046 being exploited in the wild.

**How severe is CVE-2026-50046?** Medium severity, with a CVSS score of 5.9, published 22 July 2026.

**Which products and versions are affected?** NLnet Labs Unbound 1.15.0 up to and including 1.25.1.

**Is there a fix for CVE-2026-50046?** A patch was published on 2026-07-22: Fixed in Unbound 1.25.2 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-50046 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-50046?** 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 (CWE-416) vulnerability exists in Unbound's DNS-over-TLS (DoT) forwarding logic. The TLS server name string is owned by the 'serviced_query' struct but is also referenced by the 'waiting_tcp' struct. If a query is 'jostled' (evicted) from the internal mesh during a DoT TCP handshake, the memory for the server name is freed; a subsequent TLS error causes a read-only dereference of this freed pointer, crashing the daemon. Exploitation requires the Unbound instance to have a stub or forward zone configured for DoT with an '#authname' suffix. An attacker must time queries to coincide with high server pressure and transient connection failures to trigger the vulnerable path. The issue is fixed in version 1.25.2.

## Affected products

- NLnet Labs Unbound 1.15.0 up to and including 1.25.1

## Timeline

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

## References

- [https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-50046.txt](https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-50046.txt)

## Related threats

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- [NLnet Labs Unbound DNS decompression CPU exhaustion](https://junglewise.ai/threats/cve-2026-96405-nlnet-labs-unbound-up-to-and-including-version-1-26-1-limits)
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- [NLnet Labs Unbound cache side-channel in upstream source port probe](https://junglewise.ai/threats/cve-2026-109125-in-nlnet-labs-unbound-up-to-and-including-version-1-26-1-an)
- [NLnet Labs Unbound DNS complexity attacks via ReTrap](https://junglewise.ai/threats/cve-2026-85501-nlnet-labs-unbound-dns-complexity-attacks-via-retrap)