CVE-2002-1104 in VPN Client
Summary
by MITRE
Cisco Virtual Private Network (VPN) Client software 2.x.x and 3.x before 3.0.5 allows remote attackers to cause a denial of service (crash) via TCP packets with source and destination ports of 137 (NETBIOS).
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Analysis
by VulDB Data Team • 04/19/2019
The vulnerability described in CVE-2002-1104 affects Cisco Virtual Private Network VPN Client software versions 2.x.x and 3.x before 3.0.5, representing a critical denial of service flaw that can be exploited remotely by attackers. This vulnerability specifically targets the client software's handling of TCP packets with source and destination ports set to 137, which corresponds to the NETBIOS name service port. The issue stems from inadequate input validation and packet processing logic within the VPN client implementation, creating a condition where malformed network traffic can trigger unexpected behavior in the client application.
The technical flaw manifests when the Cisco VPN client receives TCP packets with both source and destination ports configured to 137, which is a well-known port used by NETBIOS services. This particular port configuration creates a scenario where the client software fails to properly handle the packet structure, leading to a crash or complete application termination. The vulnerability operates at the network protocol level, specifically within the TCP/IP stack processing capabilities of the VPN client software, making it particularly dangerous as it can be triggered through standard network traffic without requiring authentication or privileged access. This type of flaw falls under CWE-129, which represents improper validation of the length of input data, and can be categorized as a buffer overflow or memory corruption vulnerability.
The operational impact of this vulnerability is significant for organizations relying on Cisco VPN clients for secure remote access. When exploited, the vulnerability can cause immediate disruption to network connectivity for affected users, forcing them to manually restart their VPN client applications and potentially interrupting critical business operations. The remote exploit capability means that attackers can trigger the denial of service condition from outside the network perimeter, making it particularly dangerous for organizations with remote workers or branch offices using Cisco VPN clients. From an adversary perspective, this vulnerability aligns with ATT&CK technique T1499.004, which involves network denial of service attacks, and represents a low-effort method for causing operational disruption without requiring sophisticated attack infrastructure.
Organizations affected by this vulnerability should immediately implement mitigation strategies including applying the patched version 3.0.5 or later of the Cisco VPN client software, which contains proper input validation for TCP packet handling. Network administrators should also consider implementing firewall rules to filter or block TCP packets with both source and destination ports set to 137, particularly in environments where such packets are not legitimately required. Additionally, monitoring network traffic for unusual patterns involving port 137 traffic can help detect potential exploitation attempts. The vulnerability demonstrates the importance of proper input validation in network security software and highlights the need for comprehensive testing of protocol handling logic to prevent similar issues in other network applications.