CVE-2025-40776Network attack vector

DNS cache poisoning via ECS entropy reduction

Published Jul 16, 2025 · Updated Jul 22, 2025

Cache poisoning in affected BIND 9 Subscription Edition releases allows remote attackers to corrupt cached DNS answers via spoofed responses. An ECS-enabled caching resolver can be compelled to issue queries that narrow source-port and transaction entropy, improving the odds that forged replies bypass birthday-attack mitigations. Exposure requires recursive resolution with ecs-zones configured to send EDNS Client Subnet data; authoritative-only service is unaffected, and successful poisoning falsifies subsequent DNS resolution.

CVSS severity8.6
High
EPSS probability0.21%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cache poisoning in affected BIND 9 Subscription Edition releases allows remote attackers to corrupt cached DNS answers via spoofed responses. An ECS-enabled caching resolver can be compelled to issue queries that narrow source-port and transaction entropy, improving the odds that forged replies bypass birthday-attack mitigations. Exposure requires recursive resolution with ecs-zones configured to send EDNS Client Subnet data; authoritative-only service is unaffected, and successful poisoning falsifies subsequent DNS resolution.

The record

CVE
CVE-2025-40776
Published
Jul 16, 2025
Updated
Jul 22, 2025
Vendor
Internet Systems Consortium
Product
BIND 9
Classifications
CWE-349, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 16, 2025CVE publishedPublication date reported by the CVE source.
  2. Jul 22, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=9.11.3-S1 <=9.16.50-S1
  2. Affected versionversion=9.18.11-S1 <=9.18.37-S1
  3. Affected versionversion=9.20.9-S1 <=9.20.10-S1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Internet Systems Consortium · BIND 9version=9.11.3-S1 <=9.16.50-S1; version=9.18.11-S1 <=9.18.37-S1; version=9.20.9-S1 <=9.20.10-S1

Published CVSS scores

8.6Internet Systems ConsortiumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-349Acceptance of Extraneous Untrusted Data With Trusted Data
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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