CVE-2013-4331 in LightDM
Summary
by MITRE
Light Display Manager (aka LightDM) 1.4.x before 1.4.3, 1.6.x before 1.6.2, and 1.7.x before 1.7.14 uses 0664 permissions for the temporary .Xauthority file, which allows local users to obtain sensitive information by reading the file.
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Analysis
by VulDB Data Team • 12/25/2024
Light Display Manager (LightDM) versions 1.4.x before 1.4.3, 1.6.x before 1.6.2, and 1.7.x before 1.7.14 contained a critical security flaw in its temporary file handling mechanism that exposed sensitive authentication information to unauthorized local users. The vulnerability specifically manifested in the creation of temporary .Xauthority files with overly permissive 0664 permissions, which granted read access to all users on the system. This flaw represents a direct violation of the principle of least privilege and creates a significant attack surface for local privilege escalation and information disclosure attacks. The .Xauthority file contains critical authentication tokens and credentials necessary for X Window System access, making it a valuable target for malicious actors seeking to compromise graphical user sessions.
The technical implementation of this vulnerability stems from improper permission management during the temporary file creation process within LightDM's authentication framework. When LightDM generates the .Xauthority file for X server authentication, it fails to properly restrict file permissions, allowing any local user to read the contents of this sensitive file. This misconfiguration creates a privilege escalation vector where local users can extract authentication credentials and potentially use them to gain unauthorized access to graphical sessions or escalate their privileges. The vulnerability is classified as a weakness in file permission handling and falls under the CWE-732 category for Incorrect Permission Assignment for Critical Resource, which directly relates to improper access control mechanisms.
The operational impact of this vulnerability extends beyond simple information disclosure, as it enables local users to potentially compromise the entire graphical authentication system. Attackers could leverage the extracted .Xauthority information to bypass authentication mechanisms, access other users' graphical sessions, or perform session hijacking attacks. This vulnerability particularly affects multi-user systems where different users share the same machine, creating a scenario where a less privileged user can gain access to the authentication tokens of other users. The flaw also aligns with ATT&CK technique T1078.002 for Valid Accounts: Accounts with Same Privileges, as it provides a method for local users to obtain credentials that could be used to escalate their privileges within the system.
Mitigation strategies for this vulnerability involve immediate patching of LightDM to versions 1.4.3, 1.6.2, or 1.7.14, which properly implement restrictive file permissions for temporary .Xauthority files. System administrators should also implement monitoring for unauthorized file access attempts and conduct regular security audits to verify that temporary files are created with appropriate permissions. The fix typically involves modifying the file creation process to set restrictive permissions such as 0600, ensuring that only the owner process can read the file. Additionally, organizations should consider implementing mandatory access controls and regular security assessments to prevent similar permission-related vulnerabilities from emerging in other system components. This vulnerability serves as a reminder of the critical importance of proper file permission management in authentication systems and the potential consequences of inadequate access control mechanisms.