CVE-2016-6422 in IOS
Summary
by MITRE
Cisco IOS 12.2(33)SXJ9 on Supervisor Engine 32 and 720 modules for 6500 and 7600 devices mishandles certain operators, flags, and keywords in TCAM share ACLs, which allows remote attackers to bypass intended access restrictions by sending packets that should have been recognized by a filter, aka Bug ID CSCuy64806.
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Analysis
by VulDB Data Team • 05/12/2019
The vulnerability identified as CVE-2016-6422 affects Cisco IOS software versions 12.2(33)SXJ9 and earlier on Supervisor Engine 32 and 720 modules deployed in Cisco 6500 and 7600 series devices. This flaw resides within the Traffic Control Access Control List (TCAM) implementation where the system fails to properly process specific operators, flags, and keywords within ACL configurations. The issue manifests when the system encounters certain combinations of these elements in TCAM share ACLs, leading to improper packet filtering behavior that undermines the intended security controls.
The technical root cause of this vulnerability stems from inadequate input validation and processing within the TCAM ACL handling mechanisms of the IOS software. When the system processes access control lists containing specific operators, flags, or keywords, it fails to correctly interpret or apply the filtering rules, resulting in a bypass condition where packets that should be blocked or restricted are allowed to pass through the network boundary. This represents a classic implementation flaw in the packet filtering engine that operates at the network layer, specifically affecting the Traffic Control Access Control List functionality. The vulnerability is categorized under CWE-119 as an improper restriction of operations within a memory buffer, and more specifically relates to CWE-254 as a weakness in the security configuration of the network device.
The operational impact of this vulnerability is significant as it allows remote attackers to circumvent access restrictions that are fundamental to network security policies. Attackers can exploit this weakness by crafting packets that contain specific combinations of operators, flags, and keywords that trigger the flawed processing path in the TCAM ACL implementation. This enables unauthorized access to network resources that should be protected by the configured access control lists, potentially leading to data exfiltration, lateral movement within the network, or complete compromise of the affected devices. The remote nature of the attack means that adversaries do not require physical access or local network privileges to exploit this vulnerability, making it particularly dangerous in enterprise environments where network segmentation is critical for security.
Organizations affected by this vulnerability should implement immediate mitigations including applying the relevant Cisco security patches and updates that address the TCAM ACL processing flaw. Network administrators should also consider implementing additional monitoring and logging mechanisms to detect anomalous packet flows that may indicate exploitation attempts. The mitigation strategy should include reviewing and validating all existing ACL configurations to identify potentially vulnerable rules that contain the problematic operators, flags, or keywords. Security teams should also conduct thorough network segmentation reviews and implement network access control measures that provide defense in depth. From an ATT&CK framework perspective, this vulnerability maps to T1071.004 for application layer protocol and T1566 for phishing techniques, as attackers may leverage this weakness to establish persistent access and exfiltrate data from network resources. Organizations should also consider implementing network behavior analysis tools to detect abnormal traffic patterns that may indicate exploitation of this vulnerability.