CVE-2025-5994 — Cache poisoning via the ECS-enabled Rebirthday Attack

Description (CNA)

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.

Affected (CNA)

Vendor / product	Versions
NLnet Labs / Unbound	affected 1.6.2 before 1.23.0

CWE

CWE-349

References

https://nlnetlabs.nl/downloads/unbound/CVE-2025-5994.txt

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.

CVE

No English description supplied.

https://lists.debian.org/debian-lts-announce/2025/08/msg00019.html