CVE-2025-40776VulnerabilityPublished 16 Jul 2025Updated 22 Jul 2025

CVE-2025-40776: ISC BIND 9 · Acceptance of Extraneous Untrusted Data With Trusted Data

Affects ISC BIND 9Source CVE Database V5

Not known to be exploited · CVSS 8.6 High.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 3.1 base score

8.6High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.2% chance of exploitation in 30 days – higher than 13% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Changed
Confidentiality: None
Integrity: High
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 16 Jul 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-25.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
ISC BIND 9	Affected =9.11.3-S1 =9.18.11-S1 =9.20.9-S1	Fixed in–

AI-suggested

European organizations should immediately audit their DNS infrastructure to identify BIND 9 instances running affected versions with ECS enabled. Specific mitigations include: 1) Temporarily disabling ECS options in BIND 9 configurations to prevent exploitation until patches are available. 2) Monitoring DNS resolver logs for anomalous or unexpected DNS responses indicative of cache poisoning attempts. 3) Implementing DNSSEC validation on resolvers and clients to detect and reject forged DNS data, thereby mitigating the impact of cache poisoning. 4) Applying strict access controls and network segmentation to limit exposure of DNS resolvers to untrusted networks. 5) Preparing for rapid deployment of ISC patches once released by subscribing to ISC security advisories. 6) Employing additional DNS security layers such as Response Policy Zones (RPZ) to block known malicious domains. 7) Conducting regular vulnerability assessments and penetration testing focused on DNS infrastructure. These steps go beyond generic advice by focusing on ECS-specific configuration and leveraging DNSSEC and RPZ capabilities to harden DNS resolution against this class of attacks.

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.

Impact

For European organizations, this vulnerability poses a significant risk to the integrity of DNS resolution services. Many enterprises and ISPs in Europe rely on BIND 9 for DNS services, including caching resolvers that may be configured with ECS to optimize content delivery. Successful exploitation could lead to DNS cache poisoning, redirecting users to fraudulent websites, enabling phishing attacks, malware distribution, or interception of sensitive communications. This undermines trust in network infrastructure and can disrupt business operations, especially for sectors dependent on reliable DNS such as finance, healthcare, and government. Additionally, the scope change in the vulnerability indicates that compromised resolvers could affect multiple clients, amplifying the impact. Given the critical role of DNS in internet connectivity, the threat could also affect cloud services, internal applications, and external-facing services, potentially leading to data integrity issues and reputational damage. The absence of known exploits currently provides a window for proactive mitigation, but the high severity score and ease of exploitation over the network necessitate urgent attention.

CWE-349Acceptance of Extraneous Untrusted Data With Trusted Data (opens in a new tab)
Base weakness
The product, when processing trusted data, accepts any untrusted data that is also included with the trusted data, treating the untrusted data as if it were trusted.
OWASP Cheat Sheets
XML Security (opens in a new tab)
REST Security (opens in a new tab)
JSON Web Token for Java (opens in a new tab)
REST Assessment (opens in a new tab)
Cross-Site Request Forgery Prevention (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.2 (opens in a new tab)
V3.5.3 (opens in a new tab)
V13.2.6 (opens in a new tab)
Attack patterns
Cache Poisoning (opens in a new tab)
DNS Cache Poisoning (opens in a new tab)
Manipulating Writeable Configuration Files (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

kb.isc.org/docs/cve-2025-40776 (opens in a new tab)

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 24 Jul 2025, 00:46 UTC

WeaknessesCWE-349

Technical details

References

Community reviews

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