CVE-2016-2088 in BIND
Summary
by MITRE
resolver.c in named in ISC BIND 9.10.x before 9.10.3-P4, when DNS cookies are enabled, allows remote attackers to cause a denial of service (INSIST assertion failure and daemon exit) via a malformed packet with more than one cookie option.
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Analysis
by VulDB Data Team • 07/10/2022
The vulnerability identified as CVE-2016-2088 affects the Internet Systems Consortium BIND DNS server version 9.10.x before 9.10.3-P4 and represents a critical denial of service flaw that can be exploited remotely. This issue specifically impacts the resolver.c component within named, which is the primary DNS server daemon of BIND. The vulnerability becomes exploitable when DNS cookies are enabled as a security feature designed to mitigate DNS cache poisoning attacks. The flaw manifests through a carefully crafted malformed packet that contains more than one cookie option, triggering an internal assertion failure that causes the named daemon to terminate unexpectedly.
The technical root cause of this vulnerability lies in the insufficient validation of DNS cookie options within the resolver.c module. When DNS cookies are enabled, the server implements a mechanism to track client requests and prevent cache poisoning by requiring clients to provide a valid cookie in their responses. However, the implementation fails to properly handle cases where multiple cookie options are present in a single DNS packet. The INSIST assertion failure occurs during the processing of these malformed packets, indicating that the server's internal consistency checks detect an unexpected state that violates expected program behavior. This assertion failure is particularly dangerous because it results in an abrupt daemon exit rather than graceful error handling, leading to complete service disruption for legitimate DNS queries.
The operational impact of this vulnerability is severe and can result in significant service degradation for organizations relying on BIND DNS servers. Attackers can exploit this flaw by sending specially crafted DNS packets with multiple cookie options to any DNS server running affected versions of BIND with DNS cookies enabled. The resulting daemon crash creates a denial of service condition that can persist until system administrators manually restart the named service or until the affected server is rebooted. This vulnerability affects any network infrastructure that depends on DNS resolution, including web servers, email systems, internal network services, and any application that relies on DNS lookups. The attack requires minimal resources and can be executed from any network location, making it particularly dangerous for public-facing DNS servers.
Organizations should immediately implement mitigations to protect against this vulnerability by upgrading to BIND version 9.10.3-P4 or later, which contains the necessary patches to properly validate DNS cookie options. The fix addresses the core issue by implementing proper validation logic that prevents the assertion failure when multiple cookie options are present in DNS packets. Additionally, administrators should consider temporarily disabling DNS cookies if immediate patching is not feasible, though this reduces protection against cache poisoning attacks. The vulnerability demonstrates the importance of proper input validation in security-critical systems and aligns with CWE-129, which covers insufficient validation of array index values. From an adversarial perspective, this vulnerability maps to ATT&CK technique T1499.004, specifically DNS tunneling and manipulation, as it exploits the DNS protocol's handling of cookies to achieve service disruption. Security teams should also implement monitoring to detect unusual patterns of DNS traffic that might indicate exploitation attempts and establish incident response procedures for rapid recovery from service disruptions.