CVE-2019-6476 in BIND
Summary
by MITRE
A defect in code added to support QNAME minimization can cause named to exit with an assertion failure if a forwarder returns a referral rather than resolving the query. This affects BIND versions 9.14.0 up to 9.14.6, and 9.15.0 up to 9.15.4.
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Analysis
by VulDB Data Team • 01/16/2024
The vulnerability described in CVE-2019-6476 represents a critical flaw in the Berkeley Internet Name Domain (BIND) software that specifically impacts versions 9.14.0 through 9.14.6 and 9.15.0 through 9.15.4. This issue stems from a code modification introduced to implement QNAME minimization functionality, which is designed to reduce the amount of information leaked during DNS queries by minimizing the amount of data sent in DNS responses. The flaw manifests when the named daemon encounters a referral response from a forwarder server instead of a direct resolution, causing the software to terminate abruptly through an assertion failure mechanism.
The technical root cause of this vulnerability lies in the improper handling of referral responses within the QNAME minimization code path. When a DNS resolver receives a referral from a forwarder, it should properly process this response and continue the resolution process rather than terminating the service. However, the implementation contains a logic error that fails to account for referral responses during the QNAME minimization process, leading to an assertion failure that causes the named process to exit. This behavior constitutes a denial of service condition that can be exploited by remote attackers who can craft specific DNS queries that trigger this code path.
From an operational perspective, this vulnerability poses significant risks to DNS infrastructure reliability and availability. The assertion failure results in an immediate service termination, which can disrupt DNS resolution services for all clients relying on the affected BIND server. This type of vulnerability is particularly concerning in enterprise environments where DNS servers serve as critical infrastructure components, as it can lead to cascading failures affecting multiple network services and applications that depend on DNS resolution. The impact extends beyond simple service disruption to potentially affecting business continuity and network operations.
The vulnerability aligns with CWE-617, which describes reachable assertion conditions, and demonstrates poor error handling practices in network services. From an attacker's perspective, this represents a straightforward denial of service vector that requires minimal skill to exploit, making it particularly dangerous in environments where such attacks could be used to disrupt services. The ATT&CK framework categorizes this vulnerability under the T1499.004 technique for network denial of service, as it directly targets the availability of network services through assertion failure mechanisms. Organizations should prioritize patching this vulnerability as it represents a clear path for attackers to cause service disruption without requiring sophisticated exploitation techniques.
Mitigation strategies should focus on immediate patching of affected BIND versions to the latest stable releases that contain the corrected QNAME minimization implementation. System administrators should also implement monitoring solutions to detect assertion failures and service terminations in DNS infrastructure, as well as consider implementing rate limiting and query filtering mechanisms to reduce the impact of potential exploitation attempts. Additionally, organizations should review their DNS configuration practices to ensure that forwarders are properly configured and that redundant DNS resolution paths are available to minimize the impact of such service disruptions.