CVE-2018-5743 in BIND
Summary
by MITRE
By design, BIND is intended to limit the number of TCP clients that can be connected at any given time. The number of allowed connections is a tunable parameter which, if unset, defaults to a conservative value for most servers. Unfortunately, the code which was intended to limit the number of simultaneous connections contained an error which could be exploited to grow the number of simultaneous connections beyond this limit. Versions affected: BIND 9.9.0 -> 9.10.8-P1, 9.11.0 -> 9.11.6, 9.12.0 -> 9.12.4, 9.14.0. BIND 9 Supported Preview Edition versions 9.9.3-S1 -> 9.11.5-S3, and 9.11.5-S5. Versions 9.13.0 -> 9.13.7 of the 9.13 development branch are also affected. Versions prior to BIND 9.9.0 have not been evaluated for vulnerability to CVE-2018-5743.
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Analysis
by VulDB Data Team • 07/20/2024
The vulnerability identified as CVE-2018-5743 represents a critical flaw in the Berkeley Internet Name Domain (BIND) software that affects multiple versions within the 9.x series. This issue specifically targets the TCP connection limiting mechanism that BIND employs to prevent resource exhaustion attacks. The flaw stems from a coding error in the implementation of the connection throttling logic, which was designed to enforce a maximum number of simultaneous TCP connections to protect servers from being overwhelmed by excessive client connections. The default configuration for this parameter is set to a conservative value that should prevent most scenarios of resource exhaustion, but the bug allows malicious actors to bypass these safeguards and establish more connections than permitted by the system configuration.
The technical nature of this vulnerability falls under CWE-131, which addresses improper handling of buffer sizes, and specifically relates to improper input validation and resource management within network service implementations. The flaw occurs in the connection tracking mechanism where the code fails to properly validate or enforce connection limits, creating a path for exploitation that allows attackers to incrementally establish more TCP connections than the configured maximum threshold. This behavior effectively undermines the fundamental security principle of resource limitation that BIND implements to protect against denial-of-service conditions and ensures that legitimate clients can access DNS services without being overwhelmed by malicious connection attempts. The vulnerability is particularly concerning because it operates at the protocol level and can be exploited without requiring elevated privileges or specialized knowledge of the internal workings of the DNS server.
The operational impact of CVE-2018-5743 extends beyond simple resource exhaustion, as it enables attackers to perform sustained denial-of-service attacks against DNS servers that are configured with default or standard connection limits. When exploited, this vulnerability allows adversaries to consume server resources at an accelerated rate, potentially leading to complete service unavailability for legitimate users. The attack vector is particularly insidious because it can be executed through normal DNS query processing, making detection more difficult and allowing attackers to maintain their connection exhaustion attack without raising immediate alarms. Network administrators who rely on BIND as their primary DNS server implementation face significant risk, as this vulnerability can be exploited by anyone who can establish TCP connections to the affected DNS server, potentially leading to cascading failures in DNS resolution across affected networks. The widespread adoption of BIND across internet infrastructure makes this vulnerability particularly dangerous, as a single compromised server can potentially impact thousands of downstream systems that depend on stable DNS resolution services.
Mitigation strategies for CVE-2018-5743 require immediate patching of affected BIND versions, with administrators prioritizing updates to versions that contain the corrected connection limiting logic. The most effective approach involves upgrading to BIND versions that have been patched to address the specific coding error in the connection tracking mechanism, typically those released after the vulnerability disclosure date. Organizations should also implement additional network-level protections such as connection rate limiting at firewalls or load balancers, which can provide additional defense-in-depth measures against exploitation attempts. Monitoring systems should be enhanced to detect unusual patterns of TCP connection establishment that may indicate exploitation attempts, particularly around the configured connection limits. Network segmentation and access control measures can help reduce the attack surface by limiting which systems can establish TCP connections to DNS servers, while also implementing proper logging and alerting mechanisms to detect anomalous connection behavior. The vulnerability also highlights the importance of regularly updating DNS server software and maintaining current security patches, as the issue was present across multiple major releases of BIND and demonstrates how seemingly minor coding errors can have significant security implications for widely deployed network infrastructure components.