CVE-2025-5994

HIGH EPSS 8.8%

Published Jul 16, 202511mo ago · Modified Jun 17, 20262w ago

8.7 CVSS 4.0

High

Published Jul 16, 2025 11mo ago

Last Modified Jun 17, 2026 2w ago

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 Details

Base Score

8.7

Exploitability

—

Impact

—

Vector string

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:U/V:C/RE:X/U:X

Attack Vector Network

Attack Complexity Low

Privileges Required None

User Interaction None

Scope X

Threat Intelligence

EPSS Exploit Probability

8.8% percentile

Exploit & Patch Status

No Known Exploit

No Patch Available

Weaknesses 1

CWE-349

References 2

lists.debian.org https://lists.debian.org/debian-lts-announce/2025/08/msg00019.html
nlnetlabs.nl https://nlnetlabs.nl/downloads/unbound/CVE-2025-5994.txt

Remediation

No remediation data recorded yet

Check vendor advisories and the NVD entry for patch availability.