Vulnerability Report

CVE-2026-54478

Title: NLnet Labs Unbound DNS Cookie Bypass

Other

Proof Of Concept

No public PoC currently indexed for CVE-2026-54478.

CWE Category CWE-290
Published Date Jul 22, 2026
Modified Date Jul 24, 2026
Exploit Status Not Found
Score 3.7 CVSS v3.1
Exploit Probability (EPSS)
0.17%

Vulnerability Summary

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.

Impacted Vendors

F
fedoraproject 1
N
nlnetlabs 1

Reference Links

https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-54478.txt
CVSS v3.1
Source Entity [email protected]
Severity LOW
3.7
Attack Vector
NETWORK
Complexity
HIGH
Privileges
N/A
Interaction
NONE
Confidentiality
N/A
Integrity
N/A
Availability
N/A
Scope
UNCHANGED
RAW VECTOR CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

Associated Attack Patterns (CAPEC)

Total: Patterns

CVE-2026-54478 Exploits & PoCs (Proof Of Concept)

No public PoCs found in our database for this CVE.

MODIFIED

Vulnerability data updated via NVD.

MODIFIED

Vulnerability data updated via NVD.

MODIFIED

Vulnerability data updated via NVD.

MODIFIED

Vulnerability data updated via NVD.

Attack Vector Matrix

Access Vector NETWORK
Complexity HIGH
Privileges N/A
Interaction NONE
CVSS Vector String CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

Affected Stack

No specific products linked.