VulnerabilityPublished 22 Oct 2025Updated 4 Nov 2025

CVE-2025-40780: ISC BIND 9 · Predictable From Observable State

Affects ISC BIND 9Source CVE Database V5

Not known to be exploited · CVSS 8.6 High.

Data as of 26 Oct 2026, 09:08 UTC

CVSS 3.1 base score

8.6High

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

EPSS: 0.4% chance of exploitation in 30 days – higher than 40% 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 22 Oct 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 26 Oct 2026.

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 =9.16.0 =9.18.0 =9.20.0 =9.21.0 =9.16.8-S1 =9.18.11-S1 =9.20.9-S1 =9.16.0 <=9.16.50 >=9.18.0 <=9.18.39 >=9.20.0 <=9.20.13 >=9.21.0 <=9.21.12	Fixed in–

AI-suggested

Organizations should immediately inventory their DNS infrastructure to identify affected BIND 9 versions. Although no patches are currently available, they should closely monitor ISC advisories and apply updates as soon as they are released. In the interim, consider deploying additional DNS security controls such as DNSSEC to cryptographically validate DNS responses and mitigate cache poisoning risks. Network-level mitigations include restricting DNS traffic to trusted sources, implementing rate limiting to detect anomalous query patterns, and using firewall rules to limit exposure of DNS servers. Employing DNS response validation and monitoring for unusual DNS traffic can help detect exploitation attempts. Organizations should also review and harden their DNS server configurations, disabling unnecessary features and ensuring logging is enabled for forensic analysis. For critical infrastructure, consider deploying redundant DNS servers with diverse software stacks to reduce single points of failure. Finally, raising awareness among IT and security teams about this vulnerability will ensure timely response and preparedness.

Description

In specific circumstances, due to a weakness in the Pseudo Random Number Generator (PRNG) that is used, it is possible for an attacker to predict the source port and query ID that BIND will use. This issue affects BIND 9 versions 9.16.0 through 9.16.50, 9.18.0 through 9.18.39, 9.20.0 through 9.20.13, 9.21.0 through 9.21.12, 9.16.8-S1 through 9.16.50-S1, 9.18.11-S1 through 9.18.39-S1, and 9.20.9-S1 through 9.20.13-S1.

Impact

For European organizations, this vulnerability poses a significant risk to the integrity and reliability of DNS infrastructure, which is foundational to internet operations. Successful exploitation can lead to DNS cache poisoning, allowing attackers to redirect users to malicious websites, intercept confidential communications, or disrupt access to critical services. This can result in data breaches, financial fraud, loss of customer trust, and operational downtime. Given the widespread use of BIND 9 in ISPs, enterprises, and government networks across Europe, the potential attack surface is large. Critical sectors such as finance, healthcare, telecommunications, and government services are particularly vulnerable due to their reliance on accurate DNS resolution. Additionally, the vulnerability could be leveraged in broader cyber-espionage or sabotage campaigns targeting European infrastructure. The absence of known exploits in the wild currently provides a window for proactive mitigation, but the high severity and ease of exploitation demand urgent attention.

Summary

CVE-2025-40780 identifies a critical vulnerability in ISC BIND 9, a widely deployed DNS server software. The root cause is a weakness in the pseudo-random number generator (PRNG) used by BIND to select source ports and query IDs for DNS requests. Normally, unpredictability in these values is essential to prevent DNS cache poisoning attacks, where an attacker injects forged DNS responses to redirect or intercept traffic. Due to the PRNG weakness, attackers can predict these values, allowing them to craft spoofed DNS responses that appear legitimate to the server. This vulnerability affects multiple BIND 9 versions, including 9.16.0 through 9.16.50, 9.18.0 through 9.18.39, 9.20.0 through 9.20.13, 9.21.0 through 9.21.12, and their respective S1 variants. Exploitation requires no privileges or user interaction and can be performed remotely over the network. The vulnerability impacts the integrity of DNS responses, potentially enabling attackers to redirect users to malicious sites, intercept sensitive data, or disrupt services. Although no exploits have been reported in the wild yet, the high CVSS score of 8.6 reflects the severity and ease of exploitation. ISC has not yet published patches at the time of this report, so organizations must monitor for updates. The vulnerability is classified under CWE-341 (Predictable from Observable State), indicating the PRNG's predictability is the core issue. This flaw undermines the fundamental security assumptions of DNS query randomness, making it a critical concern for any organization relying on BIND 9 for DNS resolution.

CWE-341Predictable from Observable State (opens in a new tab)
Base weakness
A number or object is predictable based on observations that the attacker can make about the state of the system or network, such as time, process ID, etc.
Implementation
Increase the entropy used to seed a PRNG.
Architecture and Design · Requirements · Libraries or Frameworks
Use products or modules that conform to FIPS 140-2 to avoid obvious entropy problems. Consult FIPS 140-2 Annex C ("Approved Random Number Generators").
Implementation
Use a PRNG that periodically re-seeds itself using input from high-quality sources, such as hardware devices with high entropy. However, do not re-seed too frequently, or else the entropy source might block.
OWASP Cheat Sheets
Forgot Password (opens in a new tab)
OWASP ASVS 4.0.3
V2.3.1 (opens in a new tab)
V2.6.2 (opens in a new tab)
V2.7.6 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 4 Nov 2025, 21:47 UTC

WeaknessesCWE-341

Technical details

References

Community reviews

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