Is CVE-2026-55990 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-55990 being exploited in the wild.

How severe is CVE-2026-55990?

Medium severity, with a CVSS score of 5.9, published 22 July 2026.

Which products and versions are affected?

NLnet Labs Unbound 1.7.0 to 1.25.1.

Is there a fix for CVE-2026-55990?

A patch was published on 2026-07-22. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-55990 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-55990?

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.

CVE-2026-55990: NLnet Labs Unbound denial of service in DNSCrypt

CVE-2026-55990 · Severity: medium · CVSS 5.9 · Published 2026-07-22

NLnet Labs Unbound, a widely used DNS resolver, contains a flaw in its DNSCrypt implementation that can lead to a service crash. If the software is configured with a specific mismatch in its security certificates and keys, a remote attacker can send a specially crafted network packet to shut down the server. This results in a denial-of-service, preventing users from resolving domain names and potentially disrupting internet connectivity for affected networks.

Technologies: NLnet Labs Unbound. Vendors: NLnet Labs.

Quick answers

Is CVE-2026-55990 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-55990 being exploited in the wild.
How severe is CVE-2026-55990?: Medium severity, with a CVSS score of 5.9, published 22 July 2026.
Which products and versions are affected?: NLnet Labs Unbound 1.7.0 to 1.25.1.
Is there a fix for CVE-2026-55990?: A patch was published on 2026-07-22. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-55990 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-55990?: 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 vulnerability exists in Unbound's DNSCrypt implementation (CWE-457) when the number of 'dnscrypt-provider-cert' files exceeds the number of 'dnscrypt-secret-key' files in the configuration. In this scenario, Unbound fails to properly initialize the tail slots of the certificate array, leaving them filled with '0xdb' bytes from the libsodium allocator. An unauthenticated remote attacker can trigger a garbage pointer dereference and subsequent daemon crash by sending a UDP datagram of at least 68 bytes starting with the '0xdb' sequence to the DNSCrypt port. This issue affects Unbound versions 1.7.0 through 1.25.1 when compiled with '--enable-dnscrypt'. The vulnerability is addressed in version 1.25.2, which introduces configuration validation and proper array initialization.

Affected products

NLnet Labs Unbound 1.7.0 to 1.25.1

Timeline

2026-07-22: advisory
2026-07-22: disclosed
2026-07-22: patched

References

https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-55990.txt

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