CVE-2019-6471 in BIND
Summary
by MITRE
A race condition which may occur when discarding malformed packets can result in BIND exiting due to a REQUIRE assertion failure in dispatch.c. Versions affected: BIND 9.11.0 -> 9.11.7, 9.12.0 -> 9.12.4-P1, 9.14.0 -> 9.14.2. Also all releases of the BIND 9.13 development branch and version 9.15.0 of the BIND 9.15 development branch and BIND Supported Preview Edition versions 9.11.3-S1 -> 9.11.7-S1.
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Analysis
by VulDB Data Team • 05/21/2025
The vulnerability identified as CVE-2019-6471 represents a critical race condition within the Internet Systems Consortium BIND DNS server software that can lead to unauthorized service disruption and potential system instability. This flaw specifically manifests during the processing of malformed network packets, where the software's packet handling mechanism encounters a timing issue that triggers an assertion failure. The race condition occurs in the dispatch.c component of BIND, which is responsible for managing incoming network traffic and routing packets to appropriate processing handlers. When malformed packets are received and processed under specific timing conditions, the software's internal state management becomes inconsistent, causing the application to terminate abruptly rather than gracefully handling the malformed input.
The technical nature of this vulnerability stems from improper synchronization mechanisms within the packet processing pipeline where multiple threads or processes may attempt to access and modify shared data structures simultaneously. This race condition creates a scenario where the software's REQUIRE assertion, designed to catch internal inconsistencies and programming errors, fails because the assertion checks are performed while the system is in an inconsistent state due to concurrent access patterns. The assertion failure in dispatch.c specifically indicates that the software encountered a condition that violates its internal assumptions about the state of data structures, leading to an immediate exit of the BIND process. This behavior fundamentally violates the expected robustness requirements for network services that should continue operating even when encountering malformed input.
The operational impact of this vulnerability extends beyond simple service interruption as it can be exploited to create denial of service conditions against DNS infrastructure. Attackers who understand the timing requirements and packet construction necessary to trigger this race condition can potentially cause BIND servers to crash repeatedly, rendering DNS resolution services unavailable to legitimate users. The vulnerability affects multiple versions of BIND across different release branches, indicating a widespread issue that has persisted through several major releases and development cycles. This widespread impact suggests that the root cause involves fundamental design patterns or implementation choices that were not properly addressed across the software's evolution, making it particularly concerning for organizations maintaining legacy DNS infrastructure. The vulnerability affects not only production releases but also development and preview editions, highlighting that the race condition exists in various stages of the software lifecycle.
Mitigation strategies for this vulnerability require immediate patch application to all affected BIND installations, as the race condition can be reliably triggered by malicious actors seeking to disrupt DNS services. Organizations should prioritize updating to the latest stable releases that contain the specific fixes for this assertion failure, as the vulnerability cannot be effectively mitigated through configuration changes alone. The fix typically involves implementing proper synchronization mechanisms to ensure that shared data structures are properly protected during concurrent access scenarios, preventing the inconsistent states that lead to assertion failures. Security teams should also implement monitoring for unexpected BIND process termination and consider implementing redundant DNS infrastructure to minimize the impact of potential exploitation attempts. This vulnerability aligns with CWE-362, which describes race conditions in concurrent programming, and may map to ATT&CK techniques involving service interruption and denial of service attacks against critical infrastructure components. The vulnerability demonstrates how seemingly minor synchronization issues in core network software can result in significant operational impacts, emphasizing the importance of thorough testing of concurrent access patterns in critical systems.