Cache poisoning via the ECS-enabled Rebirthday Attack_CVE-2025-5994

8.7 / 10

HIGH

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/R:U/V:C

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.

Basic Information

ID CVE-2025-5994

Source NLnet Labs

Published Jul 16, 2025 at 14:38

Modified Jul 16, 2025 at 15:42

Affected Product

Vendor NLnet Labs

Product Unbound

Version 1.6.2

Affected Versions NLnet Labs Unbound 1.6.2

CWE Classification

CWE-349

References

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

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