CVE-2026-54478
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.
Does this matter?
Lower severity and a low EPSS score (0.18%). Track it; it rarely justifies an emergency change on its own.
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.
- CVSS 3.1
- 3.7 LOWCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
- EPSS
- 0.18% probability · 7th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-290
- Affected
- nlnetlabs/unbound
- Source
- sep@nlnetlabs.nl
References
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.