CVE-2002-0852 in VPN Client
Summary
by MITRE
Buffer overflows in Cisco Virtual Private Network (VPN) Client 3.5.4 and earlier allows remote attackers to cause a denial of service via (1) an Internet Key Exchange (IKE) with a large Security Parameter Index (SPI) payload, or (2) an IKE packet with a large number of valid payloads.
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Analysis
by VulDB Data Team • 06/16/2019
The vulnerability described in CVE-2002-0852 represents a critical buffer overflow issue affecting Cisco Virtual Private Network VPN Client versions 3.5.4 and earlier. This flaw exists within the Internet Key Exchange protocol implementation that governs how secure connections are established between VPN clients and servers. The vulnerability stems from inadequate input validation mechanisms within the IKE processing code, specifically when handling Security Parameter Index values and payload structures. Attackers can exploit this weakness by crafting malicious IKE packets that contain oversized SPI values or excessive valid payloads, triggering memory corruption that leads to application instability.
The technical execution of this vulnerability operates through two distinct attack vectors that leverage different aspects of the IKE protocol's message handling. The first vector involves sending an IKE packet with an abnormally large Security Parameter Index payload, which exceeds the allocated buffer space in the client application's memory allocation. The second vector targets the processing of IKE packets containing a large number of valid payloads, overwhelming the client's buffer management system. Both attack methods exploit fundamental weaknesses in memory management practices and lack of proper bounds checking within the VPN client's IKE implementation. This type of vulnerability falls under CWE-121, which specifically addresses stack-based buffer overflow conditions, and represents a classic example of improper input validation that allows attackers to manipulate program execution flow.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as it can potentially allow remote attackers to disrupt network connectivity for authenticated users and administrators. When exploited successfully, the buffer overflow causes the VPN client application to crash or become unresponsive, effectively preventing legitimate users from establishing secure connections to protected networks. This disruption can have cascading effects on business operations, particularly in environments where remote access is critical for business continuity. The vulnerability is particularly concerning in enterprise environments where VPN clients are widely deployed for remote worker access, as it can be exploited by attackers without requiring authentication credentials. According to ATT&CK framework, this vulnerability maps to T1071.004 for Application Layer Protocol: DNS and T1499.004 for Endpoint Denial of Service, representing the attack patterns that leverage network protocol weaknesses for service disruption.
Mitigation strategies for CVE-2002-0852 should prioritize immediate software updates to Cisco VPN Client versions that address the buffer overflow conditions. Organizations must ensure all affected systems receive patches from Cisco, as the vulnerability exists in legacy software versions that are no longer supported. Network administrators should implement additional monitoring to detect anomalous IKE traffic patterns that might indicate exploitation attempts, particularly focusing on unusual SPI values or packets with excessive payload counts. The implementation of network segmentation and access controls can help limit the potential impact of exploitation by restricting access to vulnerable VPN client systems. Security teams should also consider deploying intrusion detection systems capable of identifying malformed IKE packets that match the vulnerability's attack patterns, providing early warning of potential exploitation attempts. Organizations should conduct thorough vulnerability assessments to identify all systems running affected VPN client versions and establish remediation schedules that prioritize critical infrastructure components.