CVE-2025-40775 in BIND
Summary
by MITRE • 05/21/2025
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.
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Analysis
by VulDB Data Team • 05/31/2025
The vulnerability described in CVE-2025-40775 represents a critical denial-of-service condition within the Berkeley Internet Name Domain (BIND) DNS server implementation. This flaw manifests when BIND processes incoming DNS protocol messages that contain Transaction Signatures (TSIG) which are used to provide authentication and integrity protection for DNS transactions. The issue specifically targets the TSIG algorithm field validation mechanism within BIND's DNS processing pipeline. When a malformed TSIG record is received with an invalid algorithm field value, the server's internal assertion checking mechanism triggers an immediate abort, causing the entire DNS service to terminate unexpectedly. This behavior affects a significant range of BIND 9 versions including the 9.20.x series from 9.20.0 through 9.20.8 and the 9.21.x series from 9.21.0 through 9.21.7, indicating a widespread impact across multiple release branches.
The technical implementation of this vulnerability stems from BIND's handling of TSIG records during DNS message processing. The assertion failure occurs during the validation phase when the server encounters an invalid algorithm field value within the TSIG structure. This represents a classic input validation error where the system fails to properly handle malformed data and instead chooses to terminate execution rather than gracefully reject the invalid message. The flaw aligns with CWE-248, which describes an unchecked exception or assertion failure that leads to program termination, and demonstrates how improper error handling can be exploited for denial-of-service attacks. The assertion failure mechanism essentially acts as an internal sanity check that BIND uses to verify the correctness of its internal state, but in this case it becomes a vector for service disruption.
The operational impact of this vulnerability extends beyond simple service interruption as it creates a potential attack surface for malicious actors seeking to disrupt DNS infrastructure. An attacker could craft malicious DNS messages with specifically crafted invalid TSIG algorithm fields to trigger the assertion failure, effectively causing the BIND server to crash and become unavailable to legitimate DNS queries. This type of attack directly maps to ATT&CK technique T1499.004, which covers network disruption through service availability attacks. The vulnerability is particularly concerning for DNS servers that are configured to accept TSIG-signed messages, as these systems become immediately vulnerable to exploitation upon receiving any malformed TSIG record regardless of whether the signature itself is valid or not. The attack requires minimal resources and sophistication, making it an attractive vector for denial-of-service attacks against critical DNS infrastructure.
Organizations affected by this vulnerability should prioritize immediate remediation through the application of security patches released by ISC, the maintainers of BIND. The most effective mitigation strategy involves upgrading to BIND versions that contain the fix for this assertion failure, typically found in versions beyond the affected ranges specified in the CVE. Network administrators should also consider implementing additional defensive measures such as rate limiting for DNS queries, monitoring for unusual TSIG-related traffic patterns, and configuring firewalls to filter suspicious DNS message patterns. The vulnerability does not appear to allow for arbitrary code execution or data compromise, but the denial-of-service impact can severely disrupt network services and potentially enable cascading failures in DNS-dependent applications. Security teams should also monitor for potential exploitation attempts through network traffic analysis and ensure that backup DNS infrastructure is available to maintain service continuity during any remediation activities.