CVE-2026-54478 DNS Cookie bypass when combined with proxy-protocol use

Low 3.7 Published 22 Jul 2026 Updated 22 Jul 2026

An off-path attacker can bypass DNS Cookie protections in Unbound when using proxy-protocol, allowing spoofed source validation.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is CVE-2026-54478?

CVE-2026-54478 is a low-severity vulnerability in Nlnetlabs Unbound, published on 22 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

In NLnet Labs Unbound 1.18.0 up to and including 1.25.1, when Unbound listens on a 'proxy-protocol-port' interface with 'answer-cookie: yes', the RFC 9018 server-cookie SipHash is computed over the proxy's wire address instead of the PROXYv2-declared client. One server cookie obtained through a given proxy node therefore validates for every PROXYv2-declared source behind that node. On a UDP+proxy-protocol front, an off-path attacker can harvest one cookie with a single legitimate query, then replay it under any spoofed source and pass DNS Cookie checks that were deployed to defeat this in the first place.

Weakness: CWE-290

Which versions are affected by CVE-2026-54478?

It affects 1 product.

Products include Nlnetlabs Unbound.

How do I fix CVE-2026-54478?

Upgrade to a fixed version.

Is CVE-2026-54478 being exploited?

There is no known exploitation of CVE-2026-54478 in the wild and no public exploit code.

All Nlnetlabs Unbound vulnerabilities

Sources

Also known as ALPINE-CVE-2026-54478, AZL-92958, DEBIAN-CVE-2026-54478, ECHO-6f24-cdd7-9e3e, GHSA-pp7x-83x2-99v7, UBUNTU-CVE-2026-54478.