CVE-2025-5994 Affecting unbound package, versions <1.23.1-r0


Severity

Recommended
low

Based on default assessment until relevant scores are available.

Threat Intelligence

EPSS
0.03% (6th percentile)

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  • Snyk IDSNYK-ALPINE322-UNBOUND-10824224
  • published19 Jul 2025
  • disclosed16 Jul 2025

Introduced: 16 Jul 2025

NewCVE-2025-5994  (opens in a new tab)

How to fix?

Upgrade Alpine:3.22 unbound to version 1.23.1-r0 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream unbound package and not the unbound package as distributed by Alpine. See How to fix? for Alpine:3.22 relevant fixed versions and status.

A multi-vendor cache poisoning vulnerability named 'Rebirthday Attack' has been discovered in caching resolvers that support EDNS Client Subnet (ECS). Unbound is also vulnerable when compiled with ECS support, i.e., '--enable-subnet', AND configured to send ECS information along with queries to upstream name servers, i.e., at least one of the 'send-client-subnet', 'client-subnet-zone' or 'client-subnet-always-forward' options is used. Resolvers supporting ECS need to segregate outgoing queries to accommodate for different outgoing ECS information. This re-opens up resolvers to a birthday paradox attack (Rebirthday Attack) that tries to match the DNS transaction ID in order to cache non-ECS poisonous replies.

CVSS Base Scores

version 3.1