CVE-2002-1103 in VPN 3000 Concentrator
Summary
by MITRE
Cisco VPN 3000 Concentrator 2.2.x, 3.6(Rel), and 3.x before 3.5.5, allows remote attackers to cause a denial of service via (1) malformed or (2) large ISAKMP packets.
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Analysis
by VulDB Data Team • 01/21/2025
The Cisco VPN 3000 Concentrator series represents a critical component in enterprise network security infrastructure, providing secure remote access and site-to-site connections for organizations worldwide. These devices operate as virtual private network gateways that establish encrypted tunnels between remote clients and corporate networks. The vulnerability described in CVE-2002-1103 specifically targets the ISAKMP (Internet Security Association and Key Management Protocol) implementation within these concentrators, which is fundamental to establishing secure connections through the IKE (Internet Key Exchange) protocol. The affected versions include 2.2.x, 3.6(Rel), and 3.x releases prior to 3.5.5, indicating a widespread issue across multiple generations of the product line that were commonly deployed in enterprise environments. This vulnerability exists within the packet processing logic of the concentrator's ISAKMP service, where proper input validation and buffer management mechanisms were insufficient to handle malformed or oversized data structures.
The technical flaw manifests when the concentrator receives ISAKMP packets that either contain malformed data structures or exceed predetermined size limits. ISAKMP packets follow a specific format defined in rfc2408 and rfc2409 standards, with defined fields for message types, exchange types, and various security parameters. When the concentrator processes these packets without adequate validation, it can encounter buffer overflows, integer overflows, or other memory corruption conditions that cause the system to crash or become unresponsive. The vulnerability can be triggered through two distinct attack vectors that exploit different aspects of packet handling. The first vector involves sending malformed ISAKMP packets that contain invalid field values or unexpected data structures, while the second vector uses oversized packets that exceed the expected buffer sizes. Both attack methods leverage the lack of proper input sanitization and boundary checking within the concentrator's ISAKMP processing engine, which operates under the common CWE-121 category of buffer overflow conditions.
The operational impact of this vulnerability extends far beyond simple service disruption, as it can severely compromise enterprise network security infrastructure and business continuity. Organizations relying on Cisco VPN 3000 Concentrators for remote access and secure communications face potential denial of service attacks that can render their entire remote connectivity infrastructure unavailable. This disruption affects employees who depend on VPN access for work, customers accessing services through secure connections, and business partners conducting transactions over encrypted tunnels. The vulnerability can be exploited remotely without requiring authentication, making it particularly dangerous as attackers can initiate attacks from anywhere on the internet. The impact on network operations can be measured in hours or days of downtime, depending on the organization's incident response capabilities and backup procedures. Security teams must also consider that this vulnerability could be used as a precursor to more sophisticated attacks, as the system instability might create opportunities for additional exploitation attempts.
Mitigation strategies for this vulnerability require immediate action from affected organizations to prevent exploitation. The primary recommended approach involves applying the vendor-supplied security patches and firmware updates that address the specific buffer overflow conditions in the ISAKMP implementation. Cisco released patches specifically targeting this vulnerability in later versions of the VPN 3000 Concentrator software, which include enhanced input validation and proper buffer management routines. Network administrators should also implement additional defensive measures such as rate limiting and packet filtering rules that can help reduce the impact of malformed packet attacks. The implementation of intrusion detection systems that can identify and block suspicious ISAKMP traffic patterns provides an additional layer of protection. Organizations should also consider implementing network segmentation to isolate VPN concentrators from critical internal systems and establishing monitoring procedures to detect unusual traffic patterns that might indicate exploitation attempts. This vulnerability aligns with ATT&CK technique T1499.004 for network denial of service and demonstrates the importance of input validation controls as outlined in CWE-787 for out-of-bounds writes. The incident highlights the critical need for proper software security practices in network infrastructure components and the necessity of regular security updates to protect against known vulnerabilities.