{"id":"CVE-2025-5994","details":"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.","modified":"2026-04-10T05:32:14.947866Z","published":"2025-07-16T15:15:33Z","related":["ALSA-2025:11849","ALSA-2025:11884","ALSA-2025:12064","openSUSE-SU-2025:15435-1"],"references":[{"type":"WEB","url":"https://nlnetlabs.nl/downloads/unbound/CVE-2025-5994.txt"}],"schema_version":"1.7.5"}