CVE-2003-0547 in GDM
Summary
by MITRE
GDM before 2.4.1.6, when using the "examine session errors" feature, allows local users to read arbitrary files via a symlink attack on the ~/.xsession-errors file.
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Analysis
by VulDB Data Team • 06/29/2021
The vulnerability described in CVE-2003-0547 represents a significant privilege escalation risk within the GNOME Display Manager (GDM) authentication system. This flaw exists in GDM versions prior to 2.4.1.6 and specifically affects the "examine session errors" functionality that administrators use to troubleshoot user session issues. The vulnerability stems from improper handling of symbolic links during file access operations, creating a path traversal condition that local attackers can exploit to gain unauthorized access to sensitive system files.
The technical implementation of this vulnerability involves a race condition and symlink manipulation attack against the ~/.xsession-errors file which is typically used by the X Window System to log session-related error information. When GDM's examine session errors feature is invoked, it attempts to read and process this file without proper validation of symbolic link integrity. An attacker can create a malicious symbolic link pointing to a sensitive file such as /etc/shadow or /etc/passwd, and when GDM processes the session errors, it follows the symlink and inadvertently reads the target file content. This represents a classic case of insecure file handling where the application does not properly validate file paths before accessing them, aligning with CWE-22 Path Traversal and CWE-367 Time-of-Check to Time-of-Use vulnerabilities.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with the ability to read arbitrary files that may contain sensitive authentication data, configuration information, or system credentials. The attack requires local system access but does not need elevated privileges, making it particularly dangerous in multi-user environments where users might have legitimate access to the system but should not be able to read other users' session error files or system configuration data. This vulnerability essentially allows an attacker to bypass normal file access controls and extract potentially sensitive information from the system. The flaw can be exploited to gather credentials, system configuration details, or other sensitive data that could be used for further attacks within the network.
Mitigation strategies for this vulnerability require immediate patching of affected GDM installations to version 2.4.1.6 or later, which includes proper symlink validation and file access controls. System administrators should also implement proper file permissions and access controls on user home directories, ensuring that session error files are not easily manipulated by unauthorized users. The solution involves implementing proper input validation and ensuring that file operations do not follow symbolic links without explicit verification of the target file's integrity and access permissions. This vulnerability demonstrates the importance of proper privilege separation and secure file handling in authentication systems, aligning with ATT&CK technique T1078 Valid Accounts and T1566 Phishing, as attackers can use such information to further compromise systems. Organizations should conduct comprehensive security audits of their display manager configurations and ensure that all authentication components properly validate file access operations to prevent similar path traversal vulnerabilities in other system components.