CVE-2002-0853 in VPN Client
Summary
by MITRE
Cisco Virtual Private Network (VPN) Client 3.5.4 and earlier allows remote attackers to cause a denial of service (CPU consumption) via a packet with a zero-length payload.
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Analysis
by VulDB Data Team • 06/25/2024
The vulnerability identified as CVE-2002-0853 affects Cisco Virtual Private Network VPN Client versions 3.5.4 and earlier, representing a significant security flaw that enables remote attackers to execute denial of service attacks through specifically crafted network packets. This vulnerability resides within the client-side implementation of Cisco's VPN software and demonstrates a critical design flaw in packet processing mechanisms. The issue manifests when the vulnerable client receives a network packet containing a zero-length payload, which triggers abnormal processing behavior that consumes excessive CPU resources.
The technical flaw stems from inadequate input validation within the VPN client's packet handling routines. When processing network traffic, the client fails to properly validate the payload length of incoming packets, specifically neglecting to handle zero-length payloads appropriately. This validation gap creates a condition where the client enters an infinite loop or excessive processing cycle when encountering such packets, leading to sustained high CPU utilization that can effectively render the system unusable. The vulnerability operates at the network protocol level and affects the client's ability to process legitimate network traffic while consuming system resources.
From an operational perspective, this vulnerability presents a substantial risk to organizations relying on Cisco VPN clients for remote access and secure communications. Attackers can exploit this weakness by simply sending a single packet with a zero-length payload to any targeted VPN client, causing immediate and sustained CPU consumption that can lead to complete system unresponsiveness. The impact extends beyond individual device compromise as it can affect network availability and user productivity, particularly in environments where VPN clients are essential for business operations. The vulnerability is particularly dangerous because it requires minimal effort to exploit and can be executed remotely without authentication.
The vulnerability aligns with CWE-129, which addresses improper validation of input length, and represents a classic example of a resource exhaustion attack pattern. It also correlates with ATT&CK technique T1499.004, which covers network denial of service attacks, and demonstrates how seemingly benign network traffic can be weaponized to compromise system availability. Organizations should prioritize immediate patching of affected systems and implement network segmentation to limit exposure. Network administrators should also consider implementing ingress filtering and monitoring for anomalous packet patterns to detect potential exploitation attempts. The vulnerability underscores the importance of robust input validation and proper error handling in network security implementations, particularly in critical infrastructure components like VPN clients that serve as primary access points for remote users.