CVE-2019-6468 in BIND
Summary
by MITRE
In BIND Supported Preview Edition, an error in the nxdomain-redirect feature can occur in versions which support EDNS Client Subnet (ECS) features. In those versions which have ECS support, enabling nxdomain-redirect is likely to lead to BIND exiting due to assertion failure. Versions affected: BIND Supported Preview Edition version 9.10.5-S1 -> 9.11.5-S5. ONLY BIND Supported Preview Edition releases are affected.
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Analysis
by VulDB Data Team • 01/07/2024
The vulnerability identified as CVE-2019-6468 represents a critical assertion failure in BIND's nxdomain-redirect feature when combined with EDNS Client Subnet (ECS) functionality. This issue specifically targets the BIND Supported Preview Edition releases, creating a scenario where legitimate DNS queries can trigger unexpected system termination. The flaw manifests when both features are enabled simultaneously, creating a condition that causes the authoritative name server to crash and exit abruptly. The technical nature of this vulnerability stems from improper handling of DNS response construction when ECS data is present during NXDOMAIN redirection operations, leading to memory corruption or invalid state conditions that trigger assertion checks within the software's internal validation mechanisms.
The operational impact of this vulnerability extends beyond simple service disruption, as it creates a potential denial of service condition that can be exploited by malicious actors to take down DNS infrastructure. When an attacker sends carefully crafted queries that combine ECS support with NXDOMAIN redirection, the server experiences an assertion failure that results in immediate termination of the BIND process. This behavior creates a cascading effect that can impact multiple domains served by the affected server, particularly in environments where DNS availability is critical for business operations. The vulnerability affects only the preview edition releases, suggesting that the issue was present in development versions but not yet addressed in stable releases, though this does not diminish the severity of the impact. The specific version range indicates that this flaw existed across a significant portion of the preview release cycle, leaving many systems exposed to potential exploitation.
Mitigation strategies for this vulnerability focus on immediate operational responses and long-term architectural considerations. Organizations should first disable the nxdomain-redirect feature when ECS support is enabled, as this combination directly triggers the assertion failure. System administrators must also consider upgrading to stable releases of BIND that have addressed this issue, as the preview editions are inherently unstable and should not be deployed in production environments. The implementation of proper monitoring and alerting systems becomes crucial to detect potential exploitation attempts, as the assertion failure may be the only indicator of an active attack. Additionally, network segmentation and access control measures should be implemented to limit exposure to potentially malicious DNS queries that could trigger this vulnerability, while maintaining compliance with industry standards such as those defined in CWE-248 for unchecked exceptions and CWE-119 for memory safety issues. The ATT&CK framework categorizes this vulnerability under the T1499.004 technique for network denial of service, emphasizing the need for robust defensive measures including proper input validation and system hardening practices to prevent exploitation of such assertion failures.