CVE-2025-40775: BIND 9 DNS TSIG DoS Vulnerability

CVE-2025-40775 Overview

When an incoming DNS protocol message includes a Transaction Signature (TSIG), BIND always checks it. If the TSIG contains an invalid value in the algorithm field, BIND immediately aborts with an assertion failure. This issue affects BIND 9 versions 9.20.0 through 9.20.8 and 9.21.0 through 9.21.7.

Critical Impact
This vulnerability causes a denial of service when exploited, leading to service disruption.

Affected Products

BIND 9.20.0 through 9.20.8
BIND 9.21.0 through 9.21.7

Discovery Timeline

2025-05-21T13:16:02.623 - CVE CVE-2025-40775 published to NVD
2025-05-23T14:15:28.880 - Last updated in NVD database

Technical Details for CVE-2025-40775

Vulnerability Analysis

CVE-2025-40775 arises from improper handling of invalid TSIG values in the algorithm field within the DNS protocol messages. This leads to an assertion failure, causing the software to terminate unexpectedly.

Root Cause

The vulnerability is caused by an assertion check on an invalid algorithm value in TSIG packets which leads to a denial of service.

Attack Vector

This vulnerability can be exploited remotely over a network by sending a specially crafted DNS request containing an invalid TSIG value.

// Example exploitation code (sanitized)
#include <stdio.h>

int main() {
    printf("Exploiting TSIG assertion failure...");
    // Code to simulate invalid TSIG packet
    return 0;
}

Detection Methods for CVE-2025-40775

Indicators of Compromise

Unexpected termination of the BIND service
Log entries showing assertion failures
High network traffic from specific IPs targeting DNS services

Detection Strategies

Monitoring for specific patterns of DNS traffic and analyzing logs for assertion failure messages can help identify exploitation attempts.

Monitoring Recommendations

Deploy network-based intrusion detection systems (NIDS) to monitor and alert on irregular DNS request patterns.

How to Mitigate CVE-2025-40775

Immediate Actions Required

Update BIND to the latest patched version.
Monitor DNS server activity closely for signs of exploitation.
Limit access to DNS services to trusted sources only.

Patch Information

Refer to the official security advisories from ISC for patch details and implement updates as they become available.

Workarounds

Currently, no effective workarounds exist for this vulnerability. Immediate patching is recommended.

bash

# Configuration example
echo "nameserver 127.0.0.1" > /etc/resolv.conf
systemctl restart bind9