CVE-2018-5734 in BIND
Summary
by MITRE
While handling a particular type of malformed packet BIND erroneously selects a SERVFAIL rcode instead of a FORMERR rcode. If the receiving view has the SERVFAIL cache feature enabled, this can trigger an assertion failure in badcache.c when the request doesn't contain all of the expected information. Affects BIND 9.10.5-S1 to 9.10.5-S4, 9.10.6-S1, 9.10.6-S2.
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Analysis
by VulDB Data Team • 07/01/2023
The vulnerability described in CVE-2018-5734 represents a critical flaw in the Berkeley Internet Name Domain (BIND) software that affects version ranges from 9.10.5-S1 through 9.10.5-S4 and 9.10.6-S1 through 9.10.6-S2. This issue stems from improper error handling during packet processing, specifically when BIND encounters malformed DNS packets that do not conform to expected protocols. The flaw manifests when the system processes certain types of malformed input that should generate a FORMERR response code but instead incorrectly returns a SERVFAIL code, creating a dangerous deviation from standard DNS protocol behavior.
The technical implementation of this vulnerability occurs within the badcache.c component of BIND, where an assertion failure triggers when a malformed packet lacks complete expected information. This assertion failure represents a fundamental breakdown in the software's error handling mechanism, as it fails to properly validate incoming packet structures before attempting to process them. The vulnerability specifically exploits the interaction between malformed packet handling and the SERVFAIL cache feature, which is designed to cache negative responses but becomes compromised when faced with incorrectly classified error conditions. This misclassification of error codes from FORMERR to SERVFAIL creates a condition where the system attempts to process data that should never have been considered valid, leading to the assertion failure in the caching subsystem.
The operational impact of this vulnerability extends beyond simple service disruption to potentially enable denial-of-service attacks that can crash the DNS server or cause it to become unresponsive to legitimate queries. When the SERVFAIL cache feature is enabled, the system's attempt to cache the malformed response triggers the assertion failure, effectively terminating the process or rendering it unstable. This behavior aligns with CWE-248, which addresses improper exception handling, and represents a classic example of how incorrect error code selection can lead to system instability. The vulnerability demonstrates how seemingly minor protocol handling errors can cascade into critical system failures, particularly when combined with caching mechanisms that attempt to store problematic responses.
From a cybersecurity perspective, this vulnerability presents a significant risk to network infrastructure since DNS servers form the backbone of internet connectivity and name resolution services. Attackers could exploit this weakness by crafting specifically malformed DNS packets that trigger the assertion failure, potentially causing widespread service disruption across networks that rely on affected BIND versions. The vulnerability's classification under the ATT&CK framework would fall within the T1499.004 technique for Network Denial of Service, as it enables attackers to disrupt DNS services through carefully constructed packet manipulation. Organizations using affected BIND versions should immediately implement mitigations including patching to the latest stable releases, disabling SERVFAIL cache functionality if not required, and implementing network-level controls to filter malformed DNS traffic. The vulnerability underscores the critical importance of proper error handling in network services and demonstrates how protocol compliance issues can lead to system instability, making it essential for security teams to monitor and address such issues proactively across their DNS infrastructure deployments.