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.
Question to Ask Vendors:
- Can you confirm whether your systems are affected by CVE-2025-5994, and if so, what steps are you currently taking to mitigate this vulnerability?
- What is your estimated timeline for fully resolving CVE-2025-5994 in your products or services, and how will you communicate updates on this issue to us as your customer?
Recommended Actions:
- Check out the advisory links provided below.