CVE-2023-32629 in Linux
Summary
by MITRE • 07/26/2023
Local privilege escalation vulnerability in Ubuntu Kernels overlayfs ovl_copy_up_meta_inode_data skip permission checks when calling ovl_do_setxattr on Ubuntu kernels
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Analysis
by VulDB Data Team • 05/21/2026
This vulnerability represents a critical local privilege escalation flaw in Ubuntu kernel versions that utilize the overlayfs filesystem implementation. The issue stems from improper permission validation within the overlayfs subsystem, specifically affecting the ovl_copy_up_meta_inode_data function which is responsible for copying metadata during file operations in overlay filesystems. When overlayfs processes file operations, it fails to properly validate permissions before executing the ovl_do_setxattr system call, creating an exploitable condition that allows unprivileged local users to escalate their privileges to root level access. The vulnerability manifests in kernel versions where the overlayfs implementation does not adequately enforce access controls during metadata operations, particularly when copying inode data between different filesystem layers.
The technical exploitation of this vulnerability occurs through a specific code path where overlayfs attempts to copy metadata from lower layers to upper layers during file operations. The ovl_copy_up_meta_inode_data function skips necessary permission checks that should validate whether the current user context has adequate privileges to modify the target inode's extended attributes. This permission bypass allows an attacker to manipulate extended attributes on files they normally wouldn't have access to modify, effectively circumventing the kernel's mandatory access controls. The flaw is particularly dangerous because it operates within the kernel space where privilege escalation is possible, and the vulnerability exists in widely deployed Ubuntu kernel versions that are commonly used in enterprise and desktop environments. This issue directly maps to CWE-284, which addresses improper access control in software systems, and represents a classic example of privilege escalation through improper validation of user permissions.
The operational impact of this vulnerability extends beyond simple privilege escalation as it enables attackers to gain complete system control without requiring external network access or complex exploitation techniques. Once successfully exploited, the attacker can modify system files, install malicious software, establish persistence mechanisms, and potentially access sensitive data that would normally be restricted to root users. The vulnerability affects Ubuntu systems running kernel versions that implement overlayfs functionality, which includes many server and desktop configurations where overlayfs is used for containerization, union mounting, or other filesystem operations. The exploitability is relatively straightforward since it requires only local access to the system and can be automated through existing privilege escalation frameworks. Security researchers have noted that this vulnerability is particularly concerning in environments where users might have limited access but require overlayfs functionality for legitimate purposes.
Mitigation strategies for this vulnerability should focus on immediate kernel updates and system hardening measures. The primary remediation involves applying the latest Ubuntu kernel patches that address the permission validation issue in overlayfs implementations, specifically targeting the ovl_copy_up_meta_inode_data function's handling of extended attributes. System administrators should prioritize updating kernel versions to those containing the patched overlayfs implementation, typically found in Ubuntu security updates or newer kernel releases. Additionally, implementing the principle of least privilege by restricting local user access to overlayfs functionality where possible can reduce exploitation risk. Organizations should also consider disabling overlayfs if it is not required for system operations, as this eliminates the attack surface entirely. The vulnerability demonstrates the importance of proper kernel security auditing and the critical need for maintaining up-to-date system configurations to prevent exploitation through privilege escalation vectors. This issue aligns with ATT&CK technique T1068 which covers local privilege escalation through kernel vulnerabilities, emphasizing the need for comprehensive kernel security monitoring and patch management processes.