CVE-2026-54478

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.

CVSS 3.1

3.7CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS

0.2% chance of exploitation in the next 30 days; higher than 15% of CVEs (scores of 2026-10-25)

CWE

CWE-290

Published

2026-07-22

Modified

2026-10-24

Record from

the NVD, synced 2026-10-24

Affected

• nlnetlabs:unbound

References

• https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-54478.txt

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