CVE-2006-3906 in VPN 3060 Concentrator
Summary
by MITRE
Internet Key Exchange (IKE) version 1 protocol, as implemented on Cisco IOS, VPN 3000 Concentrators, and PIX firewalls, allows remote attackers to cause a denial of service (resource exhaustion) via a flood of IKE Phase-1 packets that exceed the session expiration rate. NOTE: it has been argued that this is due to a design weakness of the IKE version 1 protocol, in which case other vendors and implementations would also be affected.
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Analysis
by VulDB Data Team • 07/02/2024
The vulnerability described in CVE-2006-3906 represents a critical denial of service weakness within the Internet Key Exchange version 1 protocol implementation across multiple Cisco security appliances including IOS devices, VPN 3000 Concentrators, and PIX firewalls. This flaw exploits the fundamental design characteristics of IKEv1 rather than specific implementation bugs, making it potentially widespread across different vendors and platforms. The vulnerability specifically targets the IKE Phase-1 negotiation process where cryptographic parameters are established for secure communication between peers, creating a window of opportunity for malicious actors to exploit the protocol's resource management mechanisms.
The technical exploitation occurs through the systematic flooding of IKE Phase-1 packets that exceed the legitimate session expiration rate configured on the affected devices. This attack pattern leverages the inherent limitations in how IKEv1 handles session state management and resource allocation, particularly during the initial authentication and key exchange phases. When the system receives an excessive number of Phase-1 messages within a short timeframe, it fails to properly manage the resource consumption associated with processing these requests, leading to resource exhaustion that ultimately results in service disruption and denial of legitimate user access.
The operational impact of this vulnerability extends beyond simple service interruption, as it can effectively render Cisco security appliances completely non-functional for extended periods. Network administrators face significant challenges in identifying the source of the attack due to the legitimate nature of the IKE Phase-1 packets themselves, which makes this attack particularly insidious. The resource exhaustion affects critical system components including memory allocation, CPU processing capabilities, and session table management, causing cascading failures that can impact the entire network infrastructure relying on these security devices for protection. This vulnerability directly relates to CWE-400, which addresses "Uncontrolled Resource Consumption" and aligns with ATT&CK technique T1498, "Network Denial of Service," demonstrating how protocol-level weaknesses can be exploited to achieve system-level disruption.
Mitigation strategies for this vulnerability require a multi-layered approach that includes implementing rate limiting mechanisms at network boundaries, configuring appropriate session timeout values, and deploying intrusion detection systems capable of identifying abnormal IKE traffic patterns. Network administrators should consider implementing access control lists to restrict IKE traffic to trusted sources only, while also monitoring system resources for unusual consumption patterns that might indicate an ongoing attack. The most effective long-term solution involves migrating to IKE version 2 implementations, which address many of the design weaknesses present in IKEv1, though this requires careful planning and testing to ensure compatibility with existing network infrastructure. Additionally, implementing proper network segmentation and deploying dedicated security appliances for handling VPN traffic can help isolate the impact of such attacks and provide more granular control over resource allocation and access policies.