CVE-2025-40776

Birthday Attack against Resolvers supporting ECS

Published Jul 16, 2025 CVSS 3.1 · 8.6 High EPSS < 1% KEV · Not listed
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.

Remediation

Vendor Solution

Upgrade to the patched release most closely related to your current version of BIND 9: 9.18.38-S1 or 9.20.11-S1.


Vendor Workaround

Disable ECS in BIND by removing the `ecs-zones` option from `named.conf`.

Tracking

Sign in to view the affected projects.

Advisories

Source ID Title
EUVD EUVD EUVD-2025-21705 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.
References
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
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.
Title Birthday Attack against Resolvers supporting ECS
Weaknesses CWE-349
References
Metrics cvssV3_1

{'score': 8.6, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
isc
Published
Updated
Jul 22, 2025, 2:55 PM
Reserved
Apr 16, 2025, 8:44 AM
Status
Deferred
Published
Jul 16, 2025, 2:15 PM
Modified
Jun 17, 2026, 9:22 AM