CVE-2016-2774 in BIND
Summary
by MITRE
ISC DHCP 4.1.x before 4.1-ESV-R13 and 4.2.x and 4.3.x before 4.3.4 does not restrict the number of concurrent TCP sessions, which allows remote attackers to cause a denial of service (INSIST assertion failure or request-processing outage) by establishing many sessions.
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Analysis
by VulDB Data Team • 07/09/2022
The vulnerability identified as CVE-2016-2774 affects ISC DHCP server versions prior to specific patches, creating a significant denial of service risk through uncontrolled TCP session proliferation. This issue resides in the server's handling of concurrent TCP connections, where the system fails to implement proper limits on active session counts. The flaw specifically impacts versions 4.1.x before 4.1-ESV-R13 and 4.2.x as well as 4.3.x before 4.3.4, representing a widespread vulnerability across multiple release branches of the popular DHCP implementation. The root cause of this vulnerability can be categorized under CWE-400, which addresses unchecked resource consumption, and more specifically aligns with CWE-1321, dealing with inadequate resource limitation mechanisms.
The technical exploitation of this vulnerability occurs through the establishment of numerous concurrent TCP sessions against the DHCP server, leading to resource exhaustion that ultimately results in system instability. When attackers create an excessive number of simultaneous connections, the server's internal assertion mechanisms fail, triggering an INSIST assertion failure that terminates normal request processing operations. This behavior creates a cascading effect where legitimate network traffic cannot be properly handled, effectively rendering the DHCP service unavailable to authorized clients. The vulnerability operates at the network layer and application layer, making it particularly dangerous as it can be exploited without requiring authentication or specialized privileges.
From an operational perspective, this vulnerability presents a critical risk to network infrastructure reliability and availability. Organizations relying on ISC DHCP servers for network configuration management face potential disruption of network services, as the denial of service attack can render entire network segments inaccessible. The impact extends beyond simple service interruption, as DHCP servers typically serve as foundational network services that enable dynamic IP address assignment and network configuration distribution. The vulnerability's exploitation pattern aligns with attack techniques documented in the MITRE ATT&CK framework under the T1499 category for network denial of service, specifically targeting the availability aspect of network services. Network administrators may observe symptoms including intermittent connectivity issues, failed IP address assignments, and complete service outages during active exploitation attempts.
Mitigation strategies for CVE-2016-2774 focus primarily on applying the vendor-provided security patches that introduce proper session limiting mechanisms and connection throttling. System administrators should immediately upgrade to patched versions 4.1-ESV-R13, 4.3.4, or later releases that address the resource exhaustion issue through implemented connection limits. Additionally, network-level protections can be implemented through firewall rules that restrict the number of concurrent TCP connections to the DHCP server ports, typically UDP 67 and 68, though TCP connections may also be established during certain DHCP operations. Implementing rate limiting at the network infrastructure level and monitoring for unusual connection patterns can help detect and prevent exploitation attempts. The vulnerability demonstrates the importance of resource management in network services and highlights the need for proper input validation and connection handling in server applications, reinforcing best practices from the OWASP Top Ten and NIST cybersecurity guidelines for secure network service implementation.