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.
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Affected Vendors & Products
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History
Wed, 22 Jul 2026 15:30:00 +0000
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ssvc
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Wed, 22 Jul 2026 13:30:00 +0000
| Type | Values Removed | Values Added |
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| 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. | |
| Title | DNS Cookie bypass when combined with proxy-protocol use | |
| Weaknesses | CWE-290 | |
| References |
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| Metrics |
cvssV3_1
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Status: PUBLISHED
Assigner: NLnet Labs
Published:
Updated: 2026-07-22T14:14:47.347Z
Reserved: 2026-06-22T12:27:22.817Z
Link: CVE-2026-54478
Updated: 2026-07-22T14:14:41.664Z
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OpenCVE Enrichment
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