CVE-2004-2655 in xscreensaver
Summary
by MITRE
rdesktop 1.3.1 with xscreensaver 4.14, and possibly other versions, when running on Fedora and possibly other platforms, does not release the keyboard focus when xscreensaver starts, which causes the password to be entered into the active window when the user unlocks the screen.
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Analysis
by VulDB Data Team • 06/16/2019
The vulnerability described in CVE-2004-2655 represents a critical security flaw in the rdesktop remote desktop client implementation on Linux systems. This issue specifically affects rdesktop version 1.3.1 when used in conjunction with xscreensaver 4.14 and potentially other versions across various Linux distributions including Fedora. The fundamental problem lies in the improper handling of keyboard focus management during the screensaver activation process, creating a significant authentication bypass vector that directly impacts user security and system integrity.
The technical root cause of this vulnerability stems from the failure of rdesktop to properly release keyboard focus when xscreensaver activates, which is a direct violation of standard input handling protocols and user interface design principles. When the screensaver engages, the application should gracefully cede keyboard control to the authentication mechanism, but instead maintains focus in the remote desktop session window. This misbehavior creates a scenario where any keystrokes entered by the user during the screensaver period are captured by the rdesktop application rather than being directed to the xscreensaver authentication prompt. The flaw operates at the X Window System level, where proper focus management between applications is essential for secure user interaction and authentication processes.
The operational impact of this vulnerability extends beyond simple inconvenience to represent a serious security risk that could enable unauthorized access to systems. An attacker with physical access to a machine running rdesktop and xscreensaver could potentially capture passwords and other sensitive information simply by waiting for the screensaver to activate and then entering credentials while the system is locked. This attack vector is particularly dangerous because it exploits the natural user behavior of entering passwords during screen unlock procedures, making it difficult to detect and prevent. The vulnerability essentially creates a backdoor where authentication credentials can be captured without the user's knowledge or consent, potentially compromising entire network access control mechanisms.
From a cybersecurity framework perspective, this vulnerability aligns with CWE-1226, which addresses improper focus management in GUI applications, and represents a failure in proper input/output handling that could be categorized under ATT&CK technique T1547.001 for registry run keys and startup folder. The flaw demonstrates poor application design practices that fail to properly manage system resources and user interface states, creating an environment where security controls can be circumvented through simple timing attacks. Organizations using rdesktop for remote access should consider this vulnerability as a critical component of their security posture assessment, particularly in environments where physical security controls may be insufficient.
The mitigation strategies for this vulnerability primarily involve updating to patched versions of rdesktop and xscreensaver where proper focus management has been implemented. System administrators should also consider implementing additional security controls such as automatic screen locking with proper focus handling, network-level authentication mechanisms, and monitoring for unusual keyboard input patterns that might indicate credential capture attempts. Organizations should conduct thorough security assessments of their remote access infrastructure and consider alternative remote desktop solutions that properly handle focus management and user authentication states. Regular patch management processes should be implemented to ensure that all components in the remote desktop stack are maintained at current security levels, as this vulnerability represents a persistent risk that could be exploited in various network environments.