CVE-2013-4392 in systemd
Summary
by MITRE
systemd, when updating file permissions, allows local users to change the permissions and SELinux security contexts for arbitrary files via a symlink attack on unspecified files.
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Analysis
by VulDB Data Team • 06/09/2025
The vulnerability identified as CVE-2013-4392 resides within the systemd service manager implementation, specifically during file permission updates. This flaw represents a critical security weakness that enables local attackers to manipulate file permissions and SELinux security contexts through symlink manipulation techniques. The vulnerability affects systems where systemd is responsible for managing file access controls and security policies, particularly those utilizing SELinux for mandatory access controls. Attackers can exploit this weakness by creating malicious symbolic links that point to target files, then triggering systemd's permission update process to inadvertently modify the permissions of these target files rather than the intended symlinked locations.
The technical implementation of this vulnerability stems from insufficient validation of file paths during systemd's permission update operations. When systemd processes file permission changes, it fails to properly resolve symbolic links before applying security contexts or permission modifications. This creates a race condition scenario where an attacker can place a malicious symlink in a location that systemd will traverse during its normal operations, causing the system to apply security policies to unintended files. The flaw operates at the intersection of file system traversal and security context management, where the system's expectation of operating on specific files conflicts with the reality of symlinked targets. This vulnerability is classified under CWE-367, which addresses Time-of-Check to Time-of-Use (TOCTOU) race conditions, and specifically relates to improper handling of symbolic links in privilege escalation contexts.
The operational impact of CVE-2013-4392 extends beyond simple permission modifications to potentially compromise the entire security posture of affected systems. Local users can leverage this vulnerability to escalate privileges by modifying security contexts of critical system files, potentially gaining unauthorized access to sensitive data or system resources. The exploitation process typically involves placing symbolic links in directories that systemd monitors or manages, then triggering permission update operations through normal system activities. This attack vector is particularly dangerous in multi-user environments where attackers can manipulate files that other users expect to remain secure. The vulnerability affects systems running systemd versions that implement the flawed permission update logic, with the risk being particularly high on systems where SELinux policies are actively enforced and where systemd manages critical system files.
Mitigation strategies for this vulnerability require both immediate system hardening and long-term architectural improvements. System administrators should ensure that all systemd versions are updated to patches that properly resolve the symlink traversal issues, with particular attention to the specific permission update functions within systemd. The implementation of proper symlink resolution checks and atomic file operations can prevent the race conditions that enable this attack. Organizations should also consider implementing monitoring for suspicious symlink creation patterns and establishing more restrictive file system permissions for systemd-managed directories. From an ATT&CK framework perspective, this vulnerability maps to privilege escalation techniques using system services and TOCTOU race conditions, with potential lateral movement opportunities if attackers can manipulate critical system files. Regular security audits should verify that no malicious symlinks exist in systemd-managed paths and that proper SELinux policies are in place to limit the damage from successful exploitation attempts.