Vulnerability 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.
Related Weaknesses (CWE)
References
- https://nlnetlabs.nl/downloads/unbound/CVE-2025-5994.txt
- https://lists.debian.org/debian-lts-announce/2025/08/msg00019.html
FAQ
What is CVE-2025-5994?
CVE-2025-5994 is a documented vulnerability. 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...
How severe is CVE-2025-5994?
CVSS scoring is not yet available for CVE-2025-5994. Check NVD for updates.
Is there a patch for CVE-2025-5994?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.