CVE-2018-5740 in BIND
Summary
by MITRE
"deny-answer-aliases" is a little-used feature intended to help recursive server operators protect end users against DNS rebinding attacks, a potential method of circumventing the security model used by client browsers. However, a defect in this feature makes it easy, when the feature is in use, to experience an assertion failure in name.c. Affects BIND 9.7.0->9.8.8, 9.9.0->9.9.13, 9.10.0->9.10.8, 9.11.0->9.11.4, 9.12.0->9.12.2, 9.13.0->9.13.2.
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Analysis
by VulDB Data Team • 05/01/2023
The vulnerability described in CVE-2018-5740 resides within the Berkeley Internet Name Domain software implementation, specifically targeting the "deny-answer-aliases" feature designed to protect against DNS rebinding attacks. This feature operates as a defensive mechanism for recursive DNS servers, aiming to prevent malicious actors from exploiting DNS responses to bypass browser security models that typically protect against such attacks. The flaw manifests as an assertion failure in the name.c source file, which occurs when the problematic feature is actively enabled and processing certain DNS query responses. The affected versions span multiple release lines including BIND 9.7.0 through 9.8.8, 9.9.0 through 9.9.13, 9.10.0 through 9.10.8, 9.11.0 through 9.11.4, 9.12.0 through 9.12.2, and 9.13.0 through 9.13.2, indicating a widespread issue affecting numerous stable releases of the authoritative DNS software. This vulnerability represents a critical security flaw that could potentially allow attackers to cause denial of service conditions by triggering the assertion failure, effectively crashing the DNS server and disrupting legitimate DNS resolution services.
The technical implementation of this vulnerability stems from improper handling of DNS response data when the deny-answer-aliases feature is enabled. The assertion failure in name.c suggests that the software encounters an unexpected condition during processing of DNS records that should have been validated or handled appropriately. This type of assertion failure typically occurs when code assumes certain conditions will always hold true, but encounters data that violates those assumptions. The flaw specifically impacts recursive DNS servers that have configured this particular security feature, making it exploitable by attackers who can craft specific DNS responses that trigger the assertion failure. The vulnerability operates at the core DNS processing layer where the server handles responses from authoritative name servers, making it particularly dangerous as it can be triggered through normal DNS query processing without requiring special privileges or complex attack vectors. According to CWE classification, this vulnerability maps to CWE-611: Improper Restriction of XML External Entity Reference, which describes weaknesses in XML processing that can lead to denial of service conditions, though the specific implementation here involves DNS protocol handling rather than XML parsing.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it can potentially compromise the availability and reliability of DNS infrastructure that relies on BIND software. When the assertion failure occurs, it results in the termination of the DNS server process, effectively removing the service from operation until manual intervention occurs to restart the server. This can have cascading effects throughout networks that depend on the affected DNS server for name resolution, potentially causing widespread service disruption for end users and applications. The vulnerability is particularly concerning because it affects multiple major release lines of BIND software, meaning that organizations across various network environments and deployment scenarios could be impacted. The nature of the flaw suggests that it could be triggered through standard DNS queries, making it possible for attackers to exploit this vulnerability without requiring privileged access or specialized knowledge of the internal server architecture. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving denial of service attacks and system compromise through software exploitation, specifically targeting the DNS server infrastructure that forms a critical component of network operations.
Organizations affected by this vulnerability should immediately implement mitigations including disabling the problematic "deny-answer-aliases" feature if it is not actively required for security operations, or applying the appropriate security patches released by ISC for the affected BIND versions. The most effective immediate mitigation involves either disabling the feature entirely or upgrading to patched versions of BIND software that address the assertion failure in name.c. Additionally, network administrators should monitor DNS server logs for signs of exploitation attempts and implement proper access controls to limit the ability of unauthorized users to send crafted DNS queries that might trigger the vulnerability. The remediation approach should include comprehensive testing of patched software in non-production environments before deployment to ensure that the fixes do not introduce compatibility issues with existing DNS configurations. Organizations should also consider implementing network-level protections such as DNS query filtering and rate limiting to reduce the potential impact of exploitation attempts, while maintaining detailed monitoring of DNS server performance and stability metrics to detect any anomalous behavior that might indicate successful exploitation of the vulnerability.