CVE-2002-1749 in Windows
Summary
by MITRE
Windows 2000 Terminal Services, when using the disconnect feature of the client, does not properly lock itself if it is left idle until the screen saver activates and the user disconnects, which could allow attackers to gain administrator privileges.
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Analysis
by VulDB Data Team • 06/28/2021
This vulnerability exists in Microsoft Windows 2000 Terminal Services implementation where the security mechanisms fail to properly enforce session locking protocols during specific user interaction scenarios. The flaw manifests when a user disconnects from a Terminal Services session while the system is in an idle state, particularly after the screen saver has activated. This represents a critical security gap in the Windows authentication and session management framework that could be exploited by malicious actors to escalate privileges. The vulnerability is categorized under CWE-284 Access Control, specifically addressing improper access control mechanisms within the terminal services subsystem. According to the MITRE ATT&CK framework, this issue maps to privilege escalation techniques through session hijacking and credential abuse, as attackers can potentially leverage the unlocked session state to execute malicious code with elevated privileges.
The technical implementation flaw stems from the failure of the Terminal Services client to properly validate session state transitions when disconnecting from an idle session. When a user leaves a Terminal Services session idle until the screen saver activates and then disconnects, the system does not enforce the expected security lock mechanism that should occur upon screen saver activation. This creates a window of opportunity where the session remains accessible to unauthorized users who might attempt to log in or exploit the session state. The vulnerability is particularly dangerous because it bypasses the standard screen lock protections that should automatically secure sessions when users are not actively engaged with the system. The flaw exists at the client-side implementation level where the Terminal Services client fails to properly handle the interaction between screen saver activation, idle timeout settings, and session disconnection protocols.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass potential full system compromise and data breaches. An attacker who successfully exploits this vulnerability could gain administrative access to the target system, potentially leading to complete network infiltration and persistent access. The vulnerability is particularly concerning in enterprise environments where Terminal Services is commonly used for remote administration and user access. Attackers could leverage this weakness to maintain long-term access to systems, establish backdoors, or conduct reconnaissance activities without detection. The exploitability of this vulnerability is enhanced by the fact that it can be triggered through normal user behavior patterns, making it difficult to detect through standard security monitoring. Organizations using Windows 2000 Terminal Services are particularly at risk as this vulnerability affects a core remote access functionality that many businesses depend upon for legitimate operations.
Mitigation strategies should focus on implementing comprehensive session management policies and strengthening access control mechanisms. Organizations should configure Terminal Services to enforce automatic screen locking upon user inactivity, regardless of screen saver activation states. System administrators should implement strict session timeout policies and ensure that all Terminal Services clients are properly configured to lock sessions upon disconnection. The recommended approach includes applying Microsoft security patches and updates, configuring Group Policy settings to enforce proper session locking behaviors, and implementing additional authentication layers such as smart cards or two-factor authentication. Network segmentation and monitoring should be enhanced to detect anomalous session behavior patterns that might indicate exploitation attempts. Security teams should also consider implementing automated systems to monitor and alert on Terminal Services session states, particularly focusing on idle sessions that are disconnected without proper security lock enforcement. Regular security assessments and penetration testing should be conducted to verify that the implemented mitigations effectively address the vulnerability and prevent unauthorized privilege escalation attempts.