CVE-2023-6516 in BIND
Summary
by MITRE • 02/13/2024
To keep its cache database efficient, `named` running as a recursive resolver occasionally attempts to clean up the database. It uses several methods, including some that are asynchronous: a small chunk of memory pointing to the cache element that can be cleaned up is first allocated and then queued for later processing. It was discovered that if the resolver is continuously processing query patterns triggering this type of cache-database maintenance, `named` may not be able to handle the cleanup events in a timely manner. This in turn enables the list of queued cleanup events to grow infinitely large over time, allowing the configured `max-cache-size` limit to be significantly exceeded. This issue affects BIND 9 versions 9.16.0 through 9.16.45 and 9.16.8-S1 through 9.16.45-S1.
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Analysis
by VulDB Data Team • 03/04/2024
The vulnerability described in CVE-2023-6516 represents a critical resource exhaustion flaw within the Internet Systems Consortium BIND 9 DNS server implementation. This issue specifically impacts named processes functioning as recursive resolvers, where the DNS server's cache database management system becomes overwhelmed with cleanup operations. The flaw manifests when the resolver continuously processes query patterns that trigger cache database maintenance activities, creating a scenario where the asynchronous cleanup mechanism cannot keep pace with the volume of operations being generated. The root cause lies in the memory management approach where small chunks of memory pointing to cache elements are allocated and then queued for later processing, creating a potential bottleneck in the system's ability to handle cleanup events efficiently.
The technical implementation of this vulnerability stems from the asynchronous nature of the cache cleanup process within BIND 9's recursive resolver functionality. When the system encounters continuous query patterns that necessitate cache maintenance, the queuing mechanism for cleanup operations begins to accumulate without proper bounds checking or rate limiting. This leads to an unbounded growth in the queue of pending cleanup events, effectively allowing the memory consumption to exceed the configured maximum cache size limits. The vulnerability operates at the intersection of memory management, resource allocation, and asynchronous processing, creating a condition where legitimate system operations inadvertently cause resource exhaustion. This flaw directly relates to CWE-400, which categorizes excessive resource consumption as a fundamental security weakness, and can be mapped to ATT&CK technique T1499.001 which covers resource exhaustion attacks targeting system services.
The operational impact of CVE-2023-6516 is significant and potentially devastating for affected DNS infrastructure. Systems running affected versions of BIND 9 may experience progressive memory exhaustion, leading to system instability, service degradation, or complete service outages. The infinite growth of cleanup queues can cause the named process to consume excessive memory resources, potentially leading to system crashes or the unavailability of critical DNS resolution services. This vulnerability is particularly dangerous in environments where DNS servers handle high volumes of recursive queries, as the conditions that trigger the flaw can be easily reproduced through carefully crafted query patterns. The impact extends beyond simple performance degradation to potentially compromise the availability of DNS services that underpin internet infrastructure, affecting everything from web browsing to email delivery and other internet-dependent applications.
Mitigation strategies for CVE-2023-6516 should focus on both immediate remediation and long-term architectural improvements. The primary solution involves upgrading to BIND 9 versions that have addressed this vulnerability, specifically versions beyond the affected ranges mentioned in the CVE description. Organizations should also implement monitoring systems to detect abnormal memory usage patterns in their DNS infrastructure and establish alerting mechanisms for when cache sizes approach critical thresholds. Network administrators should consider implementing rate limiting and query filtering mechanisms to prevent the continuous triggering of cache maintenance operations. Additionally, system administrators should review and adjust the max-cache-size configuration parameters to provide more conservative limits while ensuring adequate performance for legitimate DNS resolution requests. The vulnerability highlights the importance of proper resource management in asynchronous systems and underscores the need for robust bounds checking in memory allocation and queuing mechanisms to prevent similar issues in other software components.