CVE-2025-40776 Birthday Attack against Resolvers supporting ECS
Attackers can poison the cache of a BIND 9 resolver configured with EDNS Client Subnet, leading to incorrect DNS responses.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-40776?
CVE-2025-40776 is a high-severity vulnerability in ISC BIND 9, published on 16 Jul 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
A `named` caching resolver that is configured to send ECS (EDNS Client Subnet) options may be vulnerable to a cache-poisoning attack. This issue affects BIND 9 versions 9.11.3-S1 through 9.16.50-S1, 9.18.11-S1 through 9.18.37-S1, and 9.20.9-S1 through 9.20.10-S1.
Weakness: CWE-349
Which versions are affected by CVE-2025-40776?
How do I fix CVE-2025-40776?
Upgrade to a fixed version.
Is CVE-2025-40776 being exploited?
There is no known exploitation of CVE-2025-40776 in the wild and no public exploit code.
Sources
Also known as ALPINE-CVE-2025-40776, BELL-CVE-2025-40776, GHSA-2hm8-9847-q7gc.