What’s Vulnerable › Vulnerabilities
CVE-2026-54478: DNS Cookie bypass when combined with proxy-protocol use
- Severity: low (CVSS 3.7 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.2% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-07-22 · updated 2026-10-24
- Weakness: CWE-290
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.
Affected products
- NLnet Labs Unbound: from 1.18.0 before 1.25.2 — fixed in 1.25.2
How to fix
Upgrade to a fixed version: NLnet Labs Unbound 1.25.2. Check the vendor advisory for mitigations.
References
Get alerted when CVE-2026-54478 or the next vulnerability affects your stack