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OpenAdvisories
High ALAS2-2025-2951 1 CVE

Important: unbound security update (Amazon Linux 2)

Published Jul 29, 2025 · Updated Aug 4, 2025

Summary

Package updates are available for Amazon Linux 2 that fix the following vulnerabilities: CVE-2025-5994: 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.

Fixed packages 6

ReleasePackageFixed in
Amazon Linux · 2 python2-unbound 0:1.7.3-15.amzn2.0.10
Amazon Linux · 2 python3-unbound 0:1.7.3-15.amzn2.0.10
Amazon Linux · 2 unbound 0:1.7.3-15.amzn2.0.10
Amazon Linux · 2 unbound-debuginfo 0:1.7.3-15.amzn2.0.10
Amazon Linux · 2 unbound-devel 0:1.7.3-15.amzn2.0.10
Amazon Linux · 2 unbound-libs 0:1.7.3-15.amzn2.0.10

Vulnerabilities 1

  • High 8.7

    Cache poisoning via the ECS-enabled Rebirthday Attack

    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 E…

References

  • web
    https://alas.aws.amazon.com/cve/html/CVE-2025-5994.html