CVE-2008-0001 in Linux
Summary
by MITRE
VFS in the Linux kernel before 2.6.22.16, and 2.6.23.x before 2.6.23.14, performs tests of access mode by using the flag variable instead of the acc_mode variable, which might allow local users to bypass intended permissions and remove directories.
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Analysis
by VulDB Data Team • 08/04/2019
The vulnerability described in CVE-2008-0001 represents a critical access control flaw within the Virtual File System (VFS) layer of the Linux kernel, specifically affecting versions prior to 2.6.22.16 and 2.6.23.14. This issue stems from a fundamental programming error in how the kernel handles file access mode validation, creating a pathway for local privilege escalation through directory manipulation. The flaw exists in the kernel's permission checking mechanisms where the system incorrectly utilizes a flag variable rather than the properly defined acc_mode variable during access validation processes. This misconfiguration allows malicious local users to bypass intended security restrictions and execute unauthorized directory removal operations that should otherwise be restricted based on proper access controls.
The technical implementation of this vulnerability lies within the kernel's VFS subsystem where access mode checking functions fail to properly validate permissions due to the variable swap. When the kernel processes file operations, it should consistently use the acc_mode variable to determine appropriate access levels, but due to the bug, it relies on an incorrect flag variable that does not properly reflect the intended access permissions. This error creates a scenario where directory operations that require specific permissions can be executed without proper authorization checks, fundamentally undermining the kernel's access control model. The flaw specifically affects directory removal operations, allowing attackers to delete directories they would normally not have permission to remove, thereby compromising system integrity and potentially enabling further exploitation.
The operational impact of this vulnerability extends beyond simple permission bypass, as it creates opportunities for local users to manipulate the filesystem in ways that could lead to more severe consequences. An attacker with local access can exploit this weakness to remove critical directories, potentially causing system instability or creating backdoor access points. The vulnerability operates at the kernel level, making it particularly dangerous since it bypasses traditional user-space security controls and operates with the full privileges of the kernel itself. This allows for persistent access and system compromise that could remain undetected for extended periods, especially in multi-user environments where local users might not have direct administrative access but could leverage this flaw to gain elevated privileges.
Mitigation strategies for CVE-2008-0001 primarily focus on immediate kernel version updates to patched releases that correct the variable usage error in the VFS subsystem. System administrators should prioritize updating to kernel versions 2.6.22.16 or 2.6.23.14 and later, which contain the necessary fixes that ensure proper access mode validation using the correct acc_mode variable. Additionally, organizations should implement comprehensive monitoring of file system operations and directory changes to detect potential exploitation attempts. Security hardening measures including restricting local user access where possible and implementing proper file system permissions can provide additional defense in depth. The vulnerability aligns with CWE-284 which addresses improper access control, and represents a clear violation of the principle of least privilege that is fundamental to secure system design. From an ATT&CK perspective, this vulnerability maps to privilege escalation techniques and could enable lateral movement within compromised systems, making it a significant concern for enterprise security posture management.