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Vulnerability details

CVE-2025-5994

NLnet Labs Unbound

Cache poisoning via the ECS-enabled Rebirthday Attack

CVSS 4.0
8.7High

Official 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.

CVSS scores

ScoreVersionSourceVector
8.7High 4.0 CVEProject cvelistV5 (CNA) (NLnet Labs) 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

Affected products

VendorProductVersionsSource
NLnet Labs Unbound 1.6.2 ≤ v < 1.23.0 CVEProject cvelistV5 (CNA)

References and advisories

2
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Details

Published
2025-07-16
Last updated
2025-11-03
State
Published
Assigner (CNA)
NLnet Labs

Exploit prediction (EPSS)

0.21%
Probability of exploitation in 30 days
12.4%
Percentile (among all CVEs)

SSVC assessment (CISA)

Automatable
Yes
Exploitation
None
Technical impact
Partial

Weaknesses (CWE)

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