CVE-2018-20681 in mate-screensaver
Summary
by MITRE
mate-screensaver before 1.20.2 in MATE Desktop Environment allows physically proximate attackers to view screen content and possibly control applications. By unplugging and re-plugging or power-cycling external output devices (such as additionally attached graphical outputs via HDMI, VGA, DVI, etc.) the content of a screensaver-locked session can be revealed. In some scenarios, the attacker can execute applications, such as by clicking with a mouse.
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Analysis
by VulDB Data Team • 06/23/2023
The CVE-2018-20681 vulnerability represents a critical security flaw in the mate-screensaver component of the MATE Desktop Environment affecting versions prior to 1.20.2. This vulnerability specifically targets the screen locking mechanism and demonstrates a fundamental weakness in how the system handles external display device reconnection events. The flaw allows attackers with physical proximity to bypass screen lock protections through relatively simple hardware manipulation techniques that exploit the underlying display management protocols.
The technical implementation of this vulnerability stems from improper handling of display device hot-plugging events within the mate-screensaver subsystem. When external display devices such as HDMI, VGA, or DVI monitors are physically disconnected and reconnected, or when power-cycling occurs, the system fails to properly maintain the locked state of the session. This occurs because the screensaver implementation does not adequately monitor or validate display connection states during these reconnection events. The vulnerability manifests as a failure in the authentication context management, allowing unauthorized access to previously locked desktop sessions.
From an operational perspective, this vulnerability creates a significant risk for environments where physical security cannot be guaranteed, such as shared workspaces, public computing facilities, or office environments where unauthorized individuals might have access to nearby hardware. The attack vector requires only physical proximity and basic hardware manipulation capabilities, making it particularly dangerous as it bypasses traditional software-based security controls. The impact extends beyond simple information disclosure to potentially allow full application control, as demonstrated by the ability to execute applications through mouse interactions, which represents a complete compromise of the session's security boundaries.
This vulnerability aligns with several CWE classifications including CWE-284 for improper access control and CWE-310 for cryptographic issues, though the primary concern lies in the improper handling of system state transitions. The attack pattern corresponds to techniques described in the MITRE ATT&CK framework under T1087 for account access and T1133 for external remote services, as the vulnerability essentially allows unauthorized access to a system through physical manipulation rather than network-based attacks. The remediation strategy requires immediate patching of the mate-screensaver component to version 1.20.2 or later, which includes proper handling of display device reconnection events and maintains session lock integrity. Organizations should also implement additional physical security measures and consider network-level controls to limit exposure in environments where physical access cannot be strictly controlled, particularly in public or shared computing environments where such attacks could be executed by casual observers.