# CVE-2026-97206: NLnet Labs Unbound use-after-free in DNS-over-QUIC stream cleanup

Source: https://junglewise.ai/threats/cve-2026-97206-nlnet-labs-unbound-1-22-0-up-to-and-including-version-1-26-1  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-21. Updated: 2026-10-21  
License: CC BY 4.0 with a link back

CVE-2026-97206 · Severity: high · CVSS 7.5 · Published 2026-10-21

Unbound is a DNS resolver that some organizations use to resolve domain names on their networks. A remote attacker can crash the DNS resolver by triggering a QUIC path migration that causes the resolver to free a stream while a mesh reply still holds a pointer to it, leading to a use-after-free crash. This can disrupt DNS resolution and cause service outages.

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

## Quick answers

**Is CVE-2026-97206 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-97206 being exploited in the wild.

**How severe is CVE-2026-97206?** High severity, with a CVSS score of 7.5, published 21 October 2026.

**Which products and versions are affected?** NLnet Labs Unbound 1.22.0 through 1.26.1.

**Is there a fix for CVE-2026-97206?** Yes: fixed in Unbound 1.26.2. Until then: Apply the patch manually using the patch files provided by NLnet Labs (patch_CVE-2026-97206_with.diff or patch_CVE-2026-97206.diff for Unbound 1.26.1), or upgrade to Unbound 1.26.2 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-97206 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-97206?** 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.

## How to fix

- Fixed in Unbound 1.26.2

Apply the patch manually using the patch files provided by NLnet Labs (patch_CVE-2026-97206_with.diff or patch_CVE-2026-97206.diff for Unbound 1.26.1), or upgrade to Unbound 1.26.2 or later.

## Technical details

The vulnerability is a use-after-free in Unbound's DNS-over-QUIC (DoQ) implementation under multi-threaded operation. An attacker can trigger QUIC path migration to cause stream/connection cleanup while a mesh reply retains a stale pointer to the DoQ stream; when the reply completes, dereferencing the freed pointer crashes the process. The attack is remotely reachable by any DoQ client and does not require authentication.

## Affected products

- NLnet Labs Unbound 1.22.0 through 1.26.1

## Timeline

- 2026-10-21: disclosed

## References

- [https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-97206.txt](https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-97206.txt)

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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)
- [NLnet Labs Unbound use-after-free in DNS-over-HTTPs](https://junglewise.ai/threats/cve-2026-82720-nlnet-labs-unbound-use-after-free-in-dns-over-https)