CVE-2025-5994

Summary

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 Software

Weaknesses

• CWE-349: CWE-349 Acceptance of Extraneous Untrusted Data With Trusted Data

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: none
  • Automatable: yes
  • Technical Impact: partial

CVE Program Container

Additional References

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

References

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

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