CVE-2019-3820 in gnome-shell
Summary
by MITRE
It was discovered that the gnome-shell lock screen since version 3.15.91 did not properly restrict all contextual actions. An attacker with physical access to a locked workstation could invoke certain keyboard shortcuts, and potentially other actions.
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Analysis
by VulDB Data Team • 10/03/2024
The vulnerability identified as CVE-2019-3820 affects the gnome-shell lock screen component of the GNOME desktop environment, specifically impacting versions 3.15.91 and later. This security flaw represents a critical weakness in the desktop environment's authentication and access control mechanisms, as it fails to properly restrict contextual actions when a system is locked. The issue stems from inadequate validation of user interactions during the lock screen state, creating potential attack vectors for adversaries who gain physical access to locked workstations.
The technical flaw manifests in the improper handling of keyboard shortcuts and contextual actions within the lock screen interface. When a workstation is locked, the system should enforce strict access controls to prevent unauthorized interaction with the desktop environment. However, this vulnerability allows attackers to bypass certain security restrictions through specific keyboard combinations and actions that should be disabled or restricted during the locked state. The flaw operates at the user interface level where the lock screen fails to properly intercept and disable certain input methods that could potentially escalate privileges or access restricted system functions.
The operational impact of this vulnerability is significant for organizations relying on GNOME desktop environments, particularly in scenarios where physical security is compromised. An attacker with physical access to a locked workstation could potentially invoke actions that allow them to access system resources, execute commands, or escalate privileges without proper authentication. This represents a direct violation of the fundamental security principle that locked systems should prevent unauthorized access to their functionality. The vulnerability essentially creates a backdoor through which malicious actors can bypass the lock screen security measures, potentially leading to data theft, system compromise, or further network infiltration.
This vulnerability aligns with CWE-284, which addresses improper access control, and specifically relates to inadequate restriction of actions available to a user in a locked state. The flaw demonstrates a failure in privilege separation and access control enforcement during system lock states, which is a critical requirement for maintaining system security. From an attack perspective, this vulnerability maps to ATT&CK technique T1547.001, which involves the use of system services to gain persistence or execute commands. The ability to invoke keyboard shortcuts and contextual actions during lock screen states could potentially be leveraged to execute malicious payloads or establish persistent access to the compromised system.
Mitigation strategies should include immediate patching of affected GNOME desktop environments to the latest stable releases that contain the necessary security fixes. Organizations should also implement additional physical security measures such as secure workstations, tamper-evident seals, and monitoring systems to detect unauthorized physical access attempts. System administrators should consider implementing additional security controls like automatic screen locking after inactivity periods, disabling unnecessary keyboard shortcuts in lock screen contexts, and regular security audits of desktop environment configurations. The vulnerability underscores the importance of comprehensive security testing during lock screen implementations and highlights the critical need for proper access control validation in all user interface components of desktop environments.