CVE-2015-6393 in NX-OS
Summary
by MITRE
Cisco NX-OS 4.1 through 7.3 and 11.0 through 11.2 on Nexus 2000, 3000, 3500, 5000, 5500, 5600, 6000, 7000, 7700, and 9000 devices allows remote attackers to cause a denial of service (device crash) via malformed IPv4 DHCP packets to the DHCPv4 relay agent, aka Bug IDs CSCuq39250, CSCus21733, CSCus21739, CSCut76171, and CSCux67182.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 09/22/2022
Cisco NX-OS devices running versions 4.1 through 7.3 and 11.0 through 11.2 are vulnerable to a remote denial of service condition triggered by malformed IPv4 DHCP packets delivered to the DHCPv4 relay agent functionality. This vulnerability affects a wide range of Nexus hardware platforms including 2000, 3000, 3500, 5000, 5500, 5600, 6000, 7000, 7700, and 9000 series switches. The flaw resides in the processing logic of the DHCPv4 relay agent component which fails to properly validate incoming DHCP packets before attempting to process them, leading to a device crash or complete system failure. The vulnerability is categorized under CWE-121 as a buffer overflow condition where insufficient input validation allows malformed data to corrupt memory structures within the DHCP relay agent implementation. Attackers can exploit this weakness remotely without requiring authentication credentials, making it particularly dangerous in network environments where untrusted traffic flows through affected devices.
The operational impact of this vulnerability extends beyond simple service disruption as it can lead to complete network outages when critical infrastructure switches become unavailable. Network administrators may experience extended downtime while devices reboot and recover from the crash condition, potentially affecting multiple network segments that depend on the affected switches for DHCP services. The vulnerability affects the core routing and switching functionality of the affected platforms, potentially impacting network access for end users, server communications, and critical business applications that rely on dynamic IP address allocation through DHCP. In enterprise environments where Nexus switches serve as core network infrastructure components, this vulnerability could compromise network availability and business continuity. The attack vector through DHCP relay agent processing means that even traffic originating from external networks can trigger the vulnerability, making it particularly concerning for perimeter security.
Mitigation strategies should include immediate implementation of network access controls to restrict DHCP traffic to trusted sources and deployment of firmware updates from Cisco that address the specific validation issues in the DHCPv4 relay agent. Network segmentation and filtering rules can be implemented to prevent malformed DHCP packets from reaching vulnerable devices, though this approach may impact legitimate network operations. The recommended approach involves applying Cisco security advisories and firmware patches that correct the input validation logic within the DHCP relay agent processing code. Organizations should also consider implementing network monitoring solutions to detect anomalous DHCP traffic patterns that may indicate exploitation attempts. From an ATT&CK framework perspective, this vulnerability maps to T1499.004 (Endpoint Denial of Service) and represents a significant risk for network infrastructure availability. The vulnerability demonstrates the importance of robust input validation and proper error handling in network device software implementations, particularly for critical services like DHCP relay functionality that handle untrusted network traffic. Security teams should prioritize this vulnerability for remediation due to its remote exploitability and potential for widespread service disruption across affected network infrastructure.