CVE-2025-5994
Unknown Unknown - Not Provided
BaseFortify

Publication date: 2025-07-16

Last updated on: 2025-11-03

Assigner: NLnet Labs

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.
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Meta Information
Published
2025-07-16
Last Modified
2025-11-03
Generated
2026-05-07
AI Q&A
2025-07-16
EPSS Evaluated
2026-05-05
NVD
Affected Vendors & Products
Showing 3 associated CPEs
Vendor Product Version / Range
nlnetlabs unbound 1.6.2
nlnetlabs unbound 1.23.1
nlnetlabs unbound 1.23.0
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-349 The product, when processing trusted data, accepts any untrusted data that is also included with the trusted data, treating the untrusted data as if it were trusted.
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?

The Rebirthday Attack is a multi-vendor cache poisoning vulnerability affecting caching DNS resolvers that support EDNS Client Subnet (ECS). It exploits the birthday paradox to match DNS transaction IDs and inject malicious cache entries by sending non-ECS poisonous replies. Unbound is vulnerable if compiled with ECS support and configured to send ECS information with queries. The issue arises because resolvers need to segregate outgoing queries based on ECS data, and failure to do so allows attackers to poison the cache.


How can this vulnerability impact me? :

This vulnerability can allow attackers to poison the DNS cache of vulnerable resolvers, causing them to return incorrect or malicious DNS responses. This can lead to users being redirected to fraudulent or malicious websites, potentially resulting in data theft, malware infection, or other security breaches.


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