CVE-2026-54478
LowCVSS 3.7Exploitation Probability (EPSS)
Low risk7th percentile - higher than 7% of all known CVEs
Summary
In NLnet Labs Unbound from 1.18.0 up to 1.25.1, when listening on a 'proxy-protocol-port' interface with 'answer-cookie: yes', the 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 validates for every PROXYv2-declared source behind that node. 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.
Risk Assessment
The organization is at risk of DNS attacks using spoofed source addresses that can bypass DNS Cookie protections, potentially leading to DNS cache poisoning or other attacks.
Recommendation
Update Unbound to a version later than 1.25.1 or apply a temporary workaround such as disabling 'answer-cookie' on proxy-protocol interfaces.
Original NVD description (English source)
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.