CVE-2013-4169 in Display Manager
Summary
by MITRE
GNOME Display Manager (gdm) before 2.21.1 allows local users to change permissions of arbitrary directories via a symlink attack on /tmp/.X11-unix/.
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Analysis
by VulDB Data Team • 12/25/2024
The vulnerability identified as CVE-2013-4169 represents a critical security flaw in the GNOME Display Manager (GDM) version 2.21.1 and earlier, which has significant implications for system security and privilege escalation. This vulnerability specifically affects the way GDM handles temporary files during the X11 display server initialization process, creating a window of opportunity for local attackers to manipulate the system's file permissions through symbolic link manipulation.
The technical flaw stems from improper handling of temporary directories in the /tmp/.X11-unix/ path where GDM creates symbolic links without adequate security checks. When GDM initializes the X11 display server, it creates temporary files in this location without ensuring that these files are properly secured against symlink attacks. This design oversight allows a local attacker to establish malicious symbolic links in the /tmp/.X11-unix/ directory before GDM attempts to create its own files, effectively enabling the attacker to control the target of GDM's file operations. The vulnerability is classified as a symlink race condition that falls under CWE-367, which specifically addresses time-of-check to time-of-use (TOCTOU) flaws and symlink attacks.
The operational impact of this vulnerability is substantial as it provides local attackers with the ability to escalate privileges and modify permissions of arbitrary directories on the system. An attacker can exploit this weakness to gain unauthorized access to sensitive system resources, potentially leading to complete system compromise. The vulnerability is particularly dangerous because it requires minimal privileges to exploit and can be leveraged to manipulate critical system files and directories. This type of attack aligns with ATT&CK technique T1068 which covers privilege escalation through exploitation of system vulnerabilities, and T1548.001 which involves abuse of legitimate credentials and system tools for privilege escalation.
The attack vector specifically targets the race condition in GDM's temporary file creation process, where an attacker can create symbolic links in the /tmp/.X11-unix/ directory before GDM creates its own files. This allows the attacker to redirect GDM's file operations to arbitrary locations, potentially enabling them to modify system directories or create files with elevated privileges. The vulnerability demonstrates poor security practices in temporary file handling and highlights the importance of proper file system permission management and race condition prevention in system components that handle user authentication and display management.
Mitigation strategies for this vulnerability include immediate upgrade to GDM version 2.21.1 or later where the issue has been addressed through improved temporary file handling and proper symlink validation. System administrators should also implement additional security measures such as ensuring proper permissions on the /tmp directory, monitoring for unauthorized symbolic link creation, and applying the principle of least privilege to display manager processes. The fix typically involves ensuring that temporary files are created with appropriate security attributes and that the system validates the target of symbolic links before performing file operations, which aligns with security best practices outlined in various security frameworks including the NIST Cybersecurity Framework and ISO 27001 standards for secure system development and operation.