CVE-2021-25218 in BIND
Summary
by MITRE • 08/19/2021
In BIND 9.16.19, 9.17.16. Also, version 9.16.19-S1 of BIND Supported Preview Edition When a vulnerable version of named receives a query under the circumstances described above, the named process will terminate due to a failed assertion check. The vulnerability affects only BIND 9 releases 9.16.19, 9.17.16, and release 9.16.19-S1 of the BIND Supported Preview Edition.
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Analysis
by VulDB Data Team • 08/21/2021
The vulnerability identified as CVE-2021-25218 represents a critical assertion failure in the Berkeley Internet Name Domain software commonly known as BIND. This flaw specifically impacts versions 9.16.19 and 9.17.16 of the standard BIND release, along with the specialized 9.16.19-S1 version of the BIND Supported Preview Edition. The issue manifests when the named process receives certain types of queries that trigger an internal assertion check failure, leading to an abrupt termination of the service. This represents a denial of service condition that can severely impact network infrastructure relying on DNS resolution services.
The technical nature of this vulnerability stems from an assertion check that fails during query processing within the named daemon. Assertions are typically used as debugging mechanisms to verify program correctness and catch programming errors during development. When an assertion fails in production code, it indicates that the software encountered an unexpected condition that should not have occurred under normal operating circumstances. In this case, the assertion failure causes the named process to terminate abruptly, resulting in a complete service outage for DNS resolution. The vulnerability operates at the application layer and affects the core DNS server functionality, making it particularly dangerous for network infrastructure.
The operational impact of CVE-2021-25218 extends beyond simple service interruption to potentially compromise network availability and stability. Organizations relying on affected BIND versions face the risk of unauthorized service disruption, which can cascade into broader network issues affecting critical applications and services that depend on DNS resolution. The vulnerability is particularly concerning because it can be triggered through seemingly normal DNS query traffic, making it difficult to distinguish between legitimate queries and potentially malicious exploitation attempts. This characteristic aligns with attack patterns documented in the MITRE ATT&CK framework under the service stoppage category, where adversaries may leverage such vulnerabilities to disrupt network operations.
Security practitioners should prioritize immediate mitigation of this vulnerability through version upgrades to BIND 9.16.20 or 9.17.17, which contain the necessary patches to address the assertion failure. The fix implemented in these updated versions resolves the underlying condition that causes the assertion check to fail during query processing. Organizations should also consider implementing monitoring solutions to detect unusual process termination patterns in their DNS infrastructure, as this could serve as an early warning indicator of potential exploitation attempts. Additionally, network segmentation and access controls should be reviewed to limit exposure of vulnerable DNS servers to untrusted networks. This vulnerability demonstrates the importance of maintaining current software versions and the potential for seemingly minor assertion failures to result in significant service disruptions, aligning with CWE-617 which addresses reachable assertions in software development practices.