CVE-2016-6424 in ASA
Summary
by MITRE
The DHCP Relay implementation in Cisco Adaptive Security Appliance (ASA) Software 8.4.7.29 and 9.1.7.4 allows remote attackers to cause a denial of service (interface wedge) via a crafted rate of DHCP packet transmission, aka Bug ID CSCuy66942.
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Analysis
by VulDB Data Team • 05/04/2019
The vulnerability described in CVE-2016-6424 represents a significant denial of service weakness within Cisco Adaptive Security Appliance (ASA) software versions 8.4.7.29 and 9.1.7.4. This flaw specifically targets the DHCP relay functionality that operates as a critical network service component within ASA devices. The vulnerability manifests when the system processes a specially crafted rate of DHCP packet transmissions, leading to a complete interface wedging condition that effectively renders the network communication path unusable. The issue stems from insufficient input validation and rate limiting mechanisms within the DHCP relay implementation, creating a scenario where malicious actors can exploit the system's handling of DHCP traffic to cause operational disruption.
The technical nature of this vulnerability aligns with CWE-400, which categorizes it as an "Uncontrolled Resource Consumption" or "Resource Exhaustion" weakness. The flaw operates by exploiting the ASA's DHCP relay processing logic to consume excessive system resources through manipulated packet rates, ultimately causing the affected interface to become unresponsive. This type of attack falls under the ATT&CK technique T1499.004, specifically "Endpoint Denial of Service," where adversaries target network infrastructure devices to disrupt service availability. The vulnerability demonstrates how network security appliances can be compromised through traffic manipulation rather than traditional exploitation methods, making it particularly concerning for enterprise environments where ASA devices serve as primary network security gateways.
The operational impact of this vulnerability extends beyond simple service interruption, as it can severely compromise network availability and business continuity for organizations relying on Cisco ASA appliances. When an interface becomes wedged due to this vulnerability, it affects not only the specific network segment managed by that interface but can also create cascading failures throughout the network infrastructure. The attack vector requires only remote access to transmit specially crafted DHCP packets, making it particularly dangerous as it can be executed from outside the network perimeter without requiring physical access or elevated privileges. Organizations may experience extended downtime while system administrators work to recover the affected interfaces, potentially leading to significant operational disruption and potential financial losses.
Mitigation strategies for this vulnerability should focus on implementing network traffic filtering and rate limiting mechanisms to prevent the exploitation of the DHCP relay implementation. Network administrators should consider applying the latest Cisco security patches and updates that address this specific vulnerability, as these releases typically include enhanced input validation and resource consumption controls. Implementing DHCP snooping features and configuring proper access control lists can help reduce the attack surface by limiting unauthorized DHCP packet transmission. Additionally, monitoring systems should be configured to detect unusual DHCP traffic patterns that might indicate exploitation attempts, enabling proactive response measures. The vulnerability also underscores the importance of network segmentation and implementing multiple layers of defense to prevent single points of failure in critical network infrastructure components. Organizations should regularly review their ASA configurations and update their security policies to address such weaknesses in network security appliances.