CVE-2026-54478
published 2026-07-22CVE-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…
PriorityP415low3.7CVSS 3.1
AVNACHPRNUINSUCNILAN
EPSS
0.18%
7.6th percentile
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
3 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| nlnet_labs | unbound | >= 1.18.0 < 1.25.2 | 1.25.2 |
| nlnetlabs | unbound | — | — |
| nlnetlabs | unbound | >= 1.18.0 < 1.25.2 | 1.25.2 |
CVSS provenance
nvdv3.13.7LOWCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
vendor_redhat3.7LOW
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GHSA
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 pr
ghsa_unreviewed·2026-07-22
CVE-2026-54478 [LOW] CWE-290 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 pr
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.
Red Hat
unbound: Unbound: DNS Cookie security bypass via incorrect server cookie calculation
vendor_redhat·2026-07-22·CVSS 3.7
CVE-2026-54478 [LOW] CWE-303 unbound: Unbound: DNS Cookie security bypass via incorrect server cookie calculation
unbound: Unbound: DNS Cookie security bypass via incorrect server cookie calculation
A flaw was found in Unbound. When Unbound is configured to listen on a proxy-protocol port with DNS cookies enabled, it incorrectly computes the server cookie using the proxy's network address instead of the actual client's address. This vulnerability allows an off-path attacker to harvest a valid server cookie and replay it from a spoofed source, effectively bypassing DNS Cookie security checks intended to prevent DNS spoofing.
Statement: This Low impact flaw in Unbound occurs when the DNS resolver is configured to use both `proxy-protocol-port` and `answer-cookie: yes`. The server cookie is incorrectly derived from the proxy's address, enabling an off-path attacker to bypass DNS Cookie security by repl
No detection rules found.
No public exploits indexed.
Bugzilla
CVE-2026-54478 unbound: Unbound: DNS Cookie security bypass via incorrect server cookie calculation [fedora-all]
bugzilla·2026-07-27·CVSS 3.7
CVE-2026-54478 [LOW] CVE-2026-54478 unbound: Unbound: DNS Cookie security bypass via incorrect server cookie calculation [fedora-all]
CVE-2026-54478 unbound: Unbound: DNS Cookie security bypass via incorrect server cookie calculation [fedora-all]
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.
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 w
Bugzilla
CVE-2026-54478 unbound: Unbound: DNS Cookie security bypass via incorrect server cookie calculation
bugzilla·2026-07-22·CVSS 3.7
CVE-2026-54478 [LOW] CVE-2026-54478 unbound: Unbound: DNS Cookie security bypass via incorrect server cookie calculation
CVE-2026-54478 unbound: Unbound: DNS Cookie security bypass via incorrect server cookie calculation
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.
2026-07-22
Published