CVE-2019-3825 in GDM
Summary
by MITRE
A vulnerability was discovered in gdm before 3.31.4. When timed login is enabled in configuration, an attacker could bypass the lock screen by selecting the timed login user and waiting for the timer to expire, at which time they would gain access to the logged-in user's session.
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Analysis
by VulDB Data Team • 07/06/2023
The vulnerability identified as CVE-2019-3825 resides within the GNOME Display Manager (GDM) software stack, specifically affecting versions prior to 3.31.4. This security flaw represents a critical weakness in the authentication and session management mechanisms of the GNOME desktop environment, which is widely deployed across Linux distributions including Ubuntu, Fedora, and CentOS. The vulnerability stems from improper handling of timed login functionality, creating a significant bypass opportunity for unauthorized access to user sessions.
The technical implementation of this flaw occurs when the timed login feature is enabled within GDM configuration settings. This feature is designed to automatically log in a specified user after a predetermined time interval has elapsed. However, the vulnerability manifests in the lack of proper session validation checks during the timed login process. When an attacker selects a user account that has timed login configured and waits for the timer to expire, the system fails to properly authenticate the user before granting access to the active session. This represents a classic case of insufficient access control validation, where the system assumes the user is legitimate based solely on the passage of time rather than verifying credentials or session integrity.
From an operational standpoint, this vulnerability creates a severe risk for organizations relying on GNOME desktop environments, particularly in scenarios where multiple users share systems or where sensitive data is accessed through graphical interfaces. The attack vector is relatively simple and requires minimal technical expertise, making it particularly dangerous in environments where physical access to systems may be possible. An attacker could potentially gain access to sensitive user sessions, including access to personal files, network credentials, and application data without the need for complex exploitation techniques. This vulnerability directly impacts the principle of least privilege and undermines the security boundary between authenticated and unauthenticated system states.
The mitigation strategy for CVE-2019-3825 involves immediate upgrading of GDM to version 3.31.4 or later, which includes proper session validation mechanisms and enhanced authentication checks. System administrators should also review and disable timed login functionality where it is not strictly required, particularly in environments with sensitive data or high-security requirements. Additionally, organizations should implement layered security controls including proper user session management, regular security audits, and monitoring for unauthorized access attempts. This vulnerability aligns with CWE-284, which addresses improper access control, and relates to ATT&CK technique T1547.001 for registry run keys and startup folder, as it represents an unauthorized access path through session management. Organizations should also consider implementing additional security measures such as screen lock policies, automatic session timeout configurations, and regular security patch management to prevent similar vulnerabilities from being exploited in the future.