CVE-2001-0346 in Windows
Summary
by MITRE
Handle leak in Microsoft Windows 2000 telnet service allows attackers to cause a denial of service by starting a large number of sessions and terminating them.
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Analysis
by VulDB Data Team • 05/21/2019
The vulnerability identified as CVE-2001-0346 represents a critical handle leak issue within the Microsoft Windows 2000 telnet service implementation. This flaw manifests as an insufficient resource management mechanism that fails to properly release system handles when telnet sessions are terminated, creating a persistent accumulation of unreleased handles within the operating system's memory space. The vulnerability specifically affects the telnet service component that manages concurrent user connections, where each established session consumes system resources including file handles, memory structures, and process identifiers that should be automatically reclaimed upon session termination.
The technical exploitation of this vulnerability involves initiating a substantial number of telnet connections to the target Windows 2000 system, allowing each connection to establish a valid session before abruptly terminating it. This process creates a scenario where the telnet service maintains references to handles that should have been released back to the system's resource pool, resulting in a gradual depletion of available system handles. The flaw operates at the kernel level within the Windows operating system's networking stack, specifically within the telnet service subsystem that manages connection lifecycle events and resource cleanup operations. According to CWE-478, this represents a missing default case in a switch statement or similar control structure that fails to properly handle resource deallocation, while the behavior aligns with ATT&CK technique T1499.004 for network denial of service attacks.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise system stability and availability for legitimate users. As the handle leak accumulates, the system gradually loses its ability to establish new telnet connections, ultimately leading to a complete denial of service condition where no additional users can access the telnet service. The vulnerability's severity is amplified by the fact that it requires minimal resources to exploit, making it particularly dangerous in environments where telnet services are frequently accessed or where automated scanning tools might be employed to identify and exploit vulnerable systems. Network administrators may observe increasing system response times, connection timeouts, and eventually complete service unavailability as the handle leak progresses, with the system eventually reaching a state where it cannot allocate new handles for any process, including legitimate system services.
Mitigation strategies for this vulnerability require immediate implementation of security patches from Microsoft, specifically targeting the Windows 2000 telnet service component that contains the resource management flaw. System administrators should disable the telnet service entirely on systems where it is not absolutely required, as the service represents a significant security risk beyond this specific denial of service vulnerability. Network segmentation and access control measures should be implemented to restrict telnet service access to only trusted networks and users, while monitoring systems should be deployed to detect unusual connection patterns that might indicate exploitation attempts. The recommended approach involves implementing connection rate limiting, session timeout configurations, and regular system resource monitoring to identify handle leak conditions before they result in complete service denial. Additionally, organizations should consider migrating from telnet to more secure remote access protocols such as ssh, which provide better resource management and security controls. According to Microsoft security advisory MS01-018, the proper remediation includes applying the relevant security update that addresses the handle leak in the telnet service implementation, while also implementing comprehensive network security measures to prevent unauthorized access to vulnerable systems.