CVE-2000-1111 in Windows
Summary
by MITRE
Telnet Service for Windows 2000 Professional does not properly terminate incomplete connection attempts, which allows remote attackers to cause a denial of service by connecting to the server and not providing any input.
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Analysis
by VulDB Data Team • 10/11/2025
The vulnerability described in CVE-2000-1111 represents a classic denial of service flaw within the Telnet service implementation on Windows 2000 Professional systems. This issue stems from inadequate handling of connection lifecycle management where the service fails to properly terminate incomplete connection attempts, creating a resource exhaustion scenario that can be exploited by remote attackers. The flaw specifically targets the Telnet service daemon which is responsible for accepting and managing remote terminal connections, making it a critical component for system administrators to understand and secure.
The technical root cause of this vulnerability lies in the service's connection handling logic where it does not implement proper timeout mechanisms or connection state cleanup for incomplete sessions. When an attacker establishes a connection to the Telnet service but fails to provide any input or complete the authentication process, the service maintains the connection in a limbo state indefinitely. This behavior creates a resource leak where system memory and file descriptors remain allocated to these incomplete connections, eventually leading to resource exhaustion that prevents legitimate users from establishing new connections.
From an operational perspective this vulnerability presents significant risks to system availability and can be exploited with minimal technical skill by remote attackers. The attack vector requires only a basic network connection to the target system's Telnet port, making it particularly dangerous in environments where Telnet services are exposed to untrusted networks. The impact extends beyond simple service disruption as the resource exhaustion can affect other system services that depend on the same resources, potentially creating cascading failures throughout the network infrastructure. This vulnerability aligns with CWE-400 which categorizes improper resource cleanup and CWE-119 which addresses issues with resource management and memory handling.
The attack pattern described in this CVE follows established methodologies documented in the MITRE ATT&CK framework under the T1499 category for network denial of service attacks. Attackers can leverage this vulnerability by simply connecting to the Telnet service and maintaining an idle connection, consuming system resources without performing any meaningful operations. The exploitation is particularly effective because it does not require authentication or complex attack payloads, making it a preferred method for disrupting services in environments where Telnet remains enabled and accessible. Organizations with multiple Windows 2000 Professional systems running Telnet services would be particularly vulnerable to coordinated attacks that exhaust system resources across multiple targets.
Mitigation strategies for this vulnerability should prioritize immediate service disablement or removal of the Telnet service from production environments. System administrators should implement proper network segmentation to prevent unauthorized access to Telnet ports and deploy firewall rules that limit Telnet service exposure. Additionally, implementing connection timeout mechanisms and resource monitoring can help detect and prevent exploitation attempts. The recommended remediation includes disabling the Telnet service entirely and migrating to more secure remote access protocols such as SSH which properly handle connection lifecycle management and resource cleanup. Regular security assessments should verify that Telnet services are disabled on all systems and that appropriate network controls are in place to prevent unauthorized access to these vulnerable services.