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CVE-2025-40776

Birthday Attack against Resolvers supporting ECS

HIGH

8.6

CVSS Score

Published: July 16, 2025 at 01:41 PM UTC

Updated: June 17, 2026 at 09:22 AM UTC

1 product affected across 1 vendorBIND

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Severity

HIGH8.6

Exploit prediction

EPSS 0.2%

SSVC

No known exploit

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

60%

9.11.3-S1 ≤ v ≤ 9.16.50-S19.18.11-S1 ≤ v ≤ 9.18.37-S19.20.9-S1 ≤ v ≤ 9.20.10-S19.11.3-S1 9.18.11-S1 9.20.9-S1

Vendor states this is fixed in 9.0.0 (unaffected)

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

https://kb.isc.org/docs/cve-2025-40776

References (1)

Vendor Advisory

Source: [email protected]

https://kb.isc.org/docs/cve-2025-40776

SSVC — Action Prioritization

SSVCNo known exploitAutomatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

8.6HIGHisc

Attack Vector: NETWORK
Complexity: LOW
Privileges: NONE
User Interaction: NONE
Scope: CHANGED
Confidentiality: NONE
Integrity: HIGH
Availability: NONE

Vector?

Quick Info

StatusDEFERRED

CWE

CWE-349

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