CVE-2026-54478: nlnet labs unbound Authentication Bypass by Spoofing
Vulnerability summary
CVE-2026-54478 is a low (CVSS 3.7) Authentication Bypass by Spoofing vulnerability in nlnet labs unbound. EPSS estimates a 0.24% chance of exploitation in the next 30 days, higher than 14.2% of scored vulnerabilities.
Advisory lineage
Upstream 0 · Downstream 12 · Related 9Timeline
- 22-07-2026PublishedVulnerability first disclosed.
- 22-07-2026Last modifiedVulnerability information updated.
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 metrics
5 scores · 5 sources · 1 version- OSV · AlpineEcosystem advisory · calculated3.7LowCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
- OSV · UbuntuEcosystem advisory · calculated3.7LowCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
- OSV · DebianEcosystem advisory · calculated3.7LowCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
- NVDNIST3.7LowCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
EPSS trend
Probability
0.24%
Chance of exploitation in the next 30 days
Percentile
14%
Versus all other CVEs
30-day change
+0.06 pp
From 0.18% on 19-09-2026
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Alpine1 product
- unbound≥ 1.18.0, < 1.25.2-r0
Debian1 product
- unboundAll versions (No fix recorded) | < 1.26.1-0+deb13u1 | < 1.25.2-1
Nlnet labs1 product
- unbound≥ 1.18.0, < 1.25.2
Nlnetlabs1 product
- unbound≥ 1.18.0, < 1.25.2
Ubuntu1 product
- unboundAll versions (No fix recorded)
5 vendors · 5 products
References
7 links- www.nlnetlabs.nl/downloads/unbound/CVE-2026-54478.txtVendor Advisory
