CVE-2006-4983 in Network Access Control
Summary
by MITRE
Cisco NAC allows quarantined devices to communicate over the network with (1) DNS, (2) DHCP, and (3) EAPoUDP, which allows attackers to bypass control methods by tunneling network traffic through one of these protocols.
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Analysis
by VulDB Data Team • 09/25/2017
Cisco Network Access Control (NAC) systems implement network access policies to restrict unauthorized devices from accessing network resources while enforcing security compliance. The vulnerability described in CVE-2006-4983 represents a critical flaw in the NAC enforcement mechanism that permits quarantined devices to establish communication through essential network protocols. This weakness directly undermines the fundamental security principle of network segmentation and access control that NAC solutions are designed to enforce.
The technical flaw manifests in the improper handling of network traffic from devices that have been placed in quarantine status. When a device is quarantined, it should be restricted from communicating with network resources beyond the initial authentication and remediation processes. However, this vulnerability allows unauthorized communication through three critical protocols: Domain Name System (DNS) queries, Dynamic Host Configuration Protocol (DHCP) communications, and Extensible Authentication Protocol over User Datagram Protocol (EAPoUDP) exchanges. These protocols serve as essential network infrastructure services that devices require for basic network operation and authentication processes.
The operational impact of this vulnerability is significant as it provides attackers with multiple pathways to bypass network access controls. An attacker who has gained access to a quarantined device can leverage these permitted communication channels to establish covert network connections, exfiltrate data, or pivot to other network segments. The DNS protocol allows for domain resolution and potential command and control communication, while DHCP enables network configuration updates that could provide attackers with network access. EAPoUDP communications present a particularly dangerous vector as they are used for authentication processes and could enable attackers to authenticate as legitimate users or devices.
This vulnerability aligns with CWE-693, which addresses Protection Mechanism Failure, specifically in the context of network access control mechanisms. The flaw represents a failure in the security boundary enforcement that should prevent quarantined devices from communicating with network resources. From an ATT&CK framework perspective, this vulnerability maps to techniques such as T1071.004 for Application Layer Protocol: DNS and T1566 for Phishing, as attackers can use these protocols to establish persistence and exfiltrate data. The vulnerability also relates to T1021.001 for Remote Services: Remote Desktop Protocol and T1021.002 for Remote Services: SMB/Windows Admin Shares, as it enables unauthorized network access through legitimate service channels.
Organizations should implement immediate mitigations including disabling unnecessary network protocols for quarantined devices, implementing stricter firewall rules that block communication from quarantined devices to these specific protocols, and ensuring proper network segmentation. Network administrators should also deploy monitoring solutions that can detect anomalous communications from quarantined devices and implement network access control policies that prevent the bypass of authentication and authorization mechanisms. Regular security assessments and vulnerability scanning should be conducted to identify similar flaws in network infrastructure components and ensure that security controls remain effective against evolving threats.