CVE-2015-8308 in LXDM
Summary
by MITRE
LXDM before 0.5.2 did not start X server with -auth, which allows local users to bypass authentication with X connections.
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Analysis
by VulDB Data Team • 11/10/2019
The vulnerability identified as CVE-2015-8308 affects LXDM (Lightweight X Display Manager) versions prior to 052, representing a significant security flaw in the display management system that governs user authentication and graphical session access. This issue stems from the improper configuration of X server startup parameters, specifically the absence of the -auth flag that would normally establish proper authentication mechanisms for X connections. The flaw exists within the X11 display server architecture where the display manager fails to properly secure the X server connection, creating an exploitable condition that undermines the fundamental security model of graphical user interfaces.
The technical implementation of this vulnerability resides in the LXDM daemon's execution of the X server process without specifying the authentication file path that would normally be used to validate connection requests. When the X server starts without the -auth parameter, it operates in a mode where it does not require valid authentication credentials for establishing connections, allowing any local user to connect to the X server without proper verification. This represents a direct violation of the principle of least privilege and creates an authentication bypass condition that can be exploited by malicious local users. The vulnerability aligns with CWE-284 which describes improper access control mechanisms, specifically in the context of X Window System authentication failures.
The operational impact of this vulnerability extends beyond simple privilege escalation as it enables unauthorized local users to gain access to graphical sessions and potentially execute arbitrary commands through the X server connection. Attackers can leverage this flaw to establish unauthorized graphical sessions, capture user input, access graphical applications, and potentially escalate privileges further through graphical interface exploitation techniques. The vulnerability is particularly concerning because it affects the foundational display management layer that all graphical user interfaces depend upon, making it a critical weakness in systems that rely on X11 for their graphical environments. This flaw can be exploited by any local user on the system, regardless of their initial access level, and can lead to complete compromise of graphical sessions and user data.
Mitigation strategies for CVE-2015-8308 involve updating to LXDM version 0.5.2 or later, which properly implements the -auth parameter during X server startup. System administrators should also implement additional security controls such as configuring proper file permissions on X authority files, monitoring for unauthorized X server connections, and ensuring that display managers are properly configured with secure authentication mechanisms. The fix addresses the underlying issue by ensuring that the X server is started with appropriate authentication parameters that validate connection requests. Organizations should also consider implementing the ATT&CK framework mitigation strategies for privilege escalation and credential access, particularly focusing on preventing local users from gaining unauthorized access to graphical sessions through display manager vulnerabilities. Regular security audits of display management systems and X server configurations should be conducted to identify and remediate similar authentication bypass vulnerabilities across the enterprise environment.