CVE-2025-5994

Description

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.

How to fix CVE-2025-5994

To remediate CVE-2025-5994, upgrade the affected package to a fixed version below.

• —upgrade to 1.20.0-r2 or later
• —upgrade to 1.13.1-1+deb11u5 or later

Is CVE-2025-5994 being exploited?

Low — EPSS is 0.2%, meaning exploitation activity has not been observed at scale.

Affected packages (2)

• from 0, < 1.20.0-r2
• from 0, < 1.13.1-1+deb11u5

CVSS scores

References (2)

• ADVISORYsecurity.alpinelinux.org/vuln/CVE-2025-5994
• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2025-5994