CVE-2011-0727 in gdm
Summary
by MITRE
GNOME Display Manager (gdm) 2.x before 2.32.1 allows local users to change the ownership of arbitrary files via a symlink attack on a (1) dmrc or (2) face icon file under /var/cache/gdm/.
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Analysis
by VulDB Data Team • 12/01/2024
The vulnerability identified as CVE-2011-0727 represents a critical privilege escalation flaw within the GNOME Display Manager version 2.x prior to 2.32.1. This issue stems from inadequate file handling mechanisms during the initialization process of the display manager, specifically when processing user session configuration files and graphical elements. The vulnerability affects systems running GNOME desktop environments where gdm serves as the primary authentication and session management interface, creating a significant security risk for local users who can exploit this weakness to gain elevated privileges.
The technical flaw manifests through a classic symlink attack pattern that exploits the predictable temporary file creation behavior of gdm during user session setup. When users log into systems managed by gdm, the display manager creates cache files in the /var/cache/gdm/ directory to store session preferences and user interface elements such as dmrc configuration files and face icon representations. The vulnerability occurs because gdm does not properly validate the symbolic links present in these cache directories, allowing local attackers to create malicious symlinks that point to critical system files. When gdm processes these files during normal operation, it follows the symlinks and modifies the target files with the attacker's privileges, effectively changing ownership of arbitrary system files.
This vulnerability has substantial operational impact within enterprise and desktop computing environments where GNOME is the primary desktop management solution. The local privilege escalation capability means that any user with access to the system can potentially modify critical system files, including configuration files, binaries, or other user data. The attack vector is particularly concerning because it requires minimal user interaction beyond normal login processes, and the exploitation can be automated. Security administrators face challenges in detecting such attacks since they occur during legitimate user session initialization, making them difficult to distinguish from normal system behavior. The vulnerability also impacts system integrity and availability, as attackers could potentially corrupt critical system components or establish persistent backdoors through file ownership changes.
The exploitation of this vulnerability aligns with several ATT&CK framework techniques including privilege escalation through file system permissions manipulation and persistence mechanisms. From a CWE perspective, this vulnerability maps to CWE-377: Insecure Temporary File and CWE-276: Incorrect Permission Assignment for Critical Resources, as it involves both improper handling of temporary files and incorrect file permissions. The attack scenario demonstrates how seemingly benign file processing operations can be weaponized to achieve system compromise, highlighting the importance of proper input validation and privilege separation in system components that handle user data. Organizations should implement immediate mitigations including updating to gdm version 2.32.1 or later, implementing proper file system permissions for cache directories, and monitoring for unauthorized symlink creation in critical system areas. Additionally, system administrators should consider implementing automated scanning tools to detect potential symlink attacks and establish robust auditing procedures to track file ownership changes in sensitive directories.
The broader implications of this vulnerability extend beyond immediate exploitation, as it demonstrates how display managers and session management components can become attack vectors for privilege escalation. This flaw underscores the need for comprehensive security reviews of desktop environment components, particularly those that handle user-specific data and configuration files. The vulnerability also emphasizes the importance of proper privilege separation between user processes and system management functions, as well as the necessity of implementing secure file handling practices in all system components that process user input or create temporary files. Organizations should treat this vulnerability as indicative of potential weaknesses in their overall desktop security posture and consider implementing additional layers of protection including mandatory access controls, file integrity monitoring, and regular security assessments of desktop environment components.