CVE-2026-54478: Nlnetlabs Unbound

Low severity, CVSS 3.7. EPSS: 0.2% chance of exploitation in the next 30 days.

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.

Affected products

• Nlnetlabs Unbound: from 1.18.0, before 1.25.2 (fixed in 1.25.2)

Published 2026-07-22. Last modified 2026-07-24.