CVE-2006-4982 in Network Access Control
Summary
by MITRE
Cisco NAC maintains an exception list that does not record device properties other than MAC address, which allows physically proximate attackers to bypass control methods and join a local network by spoofing the MAC address of a different type of device, as demonstrated by using the MAC address of a disconnected printer.
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Analysis
by VulDB Data Team • 09/25/2017
Cisco Network Admission Control systems implement a security mechanism that relies on device identification for access control decisions. The vulnerability exists within the exception list functionality where only MAC addresses are recorded for devices that are granted network access without full authentication. This design flaw creates a significant security gap because the system does not maintain additional device properties such as device type, operating system, or hardware characteristics that would normally be used to verify device identity. Attackers can exploit this weakness by physically positioning themselves near the target network and performing MAC address spoofing attacks against the exception list entries. The vulnerability specifically allows an attacker to impersonate a legitimate device by simply copying the MAC address of an authorized device that is currently disconnected from the network, such as a printer that has been removed from the network but whose MAC address remains in the exception list.
The technical implementation of this vulnerability stems from insufficient device validation mechanisms within Cisco NAC's admission control process. When a device attempts to connect to the network, the system checks against the exception list to determine if the device should be granted access without full authentication. However, the exception list only stores MAC addresses without maintaining context about device type, manufacturer, or other identifying characteristics. This limitation means that when an attacker spoofs the MAC address of a disconnected printer, the system cannot distinguish between a legitimate printer that is currently offline and an unauthorized device attempting to masquerade as that printer. The attack vector is particularly effective because it requires minimal technical expertise and can be executed from physical proximity to the network infrastructure, making it a low-effort, high-impact method for bypassing network access controls.
This vulnerability creates substantial operational impacts for organizations relying on Cisco NAC for network security. The ability to bypass access controls through simple MAC address spoofing undermines the fundamental security model of network admission control systems, which are designed to ensure that only authorized devices can access network resources. Attackers can gain network access without proper authentication, potentially leading to unauthorized data access, network infiltration, and lateral movement within the organization's network infrastructure. The vulnerability is particularly dangerous because it can be exploited by anyone with physical access to the network perimeter, making it a significant risk for environments where unauthorized physical access cannot be fully controlled. Organizations may experience unauthorized network access, potential data breaches, and compromised network integrity as a result of this flaw.
Organizations should implement multiple layers of mitigation strategies to address this vulnerability. The primary recommendation involves configuring Cisco NAC systems to require additional device authentication factors beyond simple MAC address validation, such as implementing 802.1X authentication or device certificate validation. Network administrators should regularly audit and purge exception lists to remove entries for devices that are no longer in use or have been disconnected from the network. Implementing network segmentation and access control lists can help limit the impact of successful attacks by restricting lateral movement. Additionally, organizations should deploy network monitoring solutions that can detect unusual MAC address changes or unauthorized access attempts. The mitigation approach should align with industry standards such as those defined in the CWE-284 access control weakness category and should consider ATT&CK framework techniques related to privilege escalation and lateral movement through network access control bypass methods. Regular security assessments and penetration testing should be conducted to identify and remediate similar weaknesses in network access control implementations.