Amazon Linux 2 Security Advisory: ALAS2-2025-2951
Advisory Released Date: 2025-08-04
Advisory Updated Date: 2025-08-04
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. (CVE-2025-5994)
Affected Packages:
unbound
Note:
This advisory is applicable to Amazon Linux 2 (AL2) Core repository. Visit this FAQ section for the difference between AL2 Core and AL2 Extras advisories.
Issue Correction:
Run yum update unbound or yum update --advisory ALAS2-2025-2951 to update your system.
aarch64:
unbound-1.7.3-15.amzn2.0.10.aarch64
unbound-devel-1.7.3-15.amzn2.0.10.aarch64
unbound-libs-1.7.3-15.amzn2.0.10.aarch64
python2-unbound-1.7.3-15.amzn2.0.10.aarch64
python3-unbound-1.7.3-15.amzn2.0.10.aarch64
unbound-debuginfo-1.7.3-15.amzn2.0.10.aarch64
i686:
unbound-1.7.3-15.amzn2.0.10.i686
unbound-devel-1.7.3-15.amzn2.0.10.i686
unbound-libs-1.7.3-15.amzn2.0.10.i686
python2-unbound-1.7.3-15.amzn2.0.10.i686
python3-unbound-1.7.3-15.amzn2.0.10.i686
unbound-debuginfo-1.7.3-15.amzn2.0.10.i686
src:
unbound-1.7.3-15.amzn2.0.10.src
x86_64:
unbound-1.7.3-15.amzn2.0.10.x86_64
unbound-devel-1.7.3-15.amzn2.0.10.x86_64
unbound-libs-1.7.3-15.amzn2.0.10.x86_64
python2-unbound-1.7.3-15.amzn2.0.10.x86_64
python3-unbound-1.7.3-15.amzn2.0.10.x86_64
unbound-debuginfo-1.7.3-15.amzn2.0.10.x86_64