CVE-2008-4210 in Linux
Summary
by MITRE
fs/open.c in the Linux kernel before 2.6.22 does not properly strip setuid and setgid bits when there is a write to a file, which allows local users to gain the privileges of a different group, and obtain sensitive information or possibly have unspecified other impact, by creating an executable file in a setgid directory through the (1) truncate or (2) ftruncate function in conjunction with memory-mapped I/O.
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Analysis
by VulDB Data Team • 12/26/2024
The vulnerability described in CVE-2008-4210 represents a critical privilege escalation flaw within the Linux kernel's file system handling mechanisms. This issue exists in kernel versions prior to 2.6.22 and specifically targets the fs/open.c component where the kernel fails to properly sanitize setuid and setgid bits during file write operations. The flaw occurs when a local user manipulates files within setgid directories through specific system calls that trigger memory-mapped I/O operations. The vulnerability stems from improper handling of file permissions during write operations, creating a pathway for privilege elevation that directly violates fundamental security principles of Unix-like systems. The technical implementation involves the kernel's failure to strip elevated permission bits when file contents are modified through truncate or ftruncate functions, allowing attackers to maintain elevated privileges beyond their intended scope.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass potential information disclosure and arbitrary code execution capabilities. When an attacker creates an executable file in a setgid directory and subsequently triggers a truncate or ftruncate operation combined with memory mapping, they can effectively bypass the normal permission checking mechanisms that should prevent such privilege escalation. This flaw allows local users to gain the privileges of the group that owns the directory, potentially enabling access to sensitive system resources or data that should be restricted to authorized users only. The vulnerability is particularly dangerous because it leverages legitimate system functions to achieve unauthorized access, making detection more difficult and exploitation more reliable. The memory-mapped I/O component adds complexity to the attack vector, as it involves direct manipulation of virtual memory mappings that can be used to maintain elevated privileges across multiple system calls.
The security implications of this vulnerability align with CWE-276, which addresses improper file permissions and inadequate access control mechanisms. This classification reflects the fundamental breakdown in the kernel's permission model where the setuid/setgid bits are not properly cleared during write operations, violating the principle of least privilege. From an attack perspective, this vulnerability maps to several ATT&CK techniques including privilege escalation through kernel exploitation and credential access through file system manipulation. The flaw demonstrates how seemingly benign system functions can be weaponized when proper security boundaries are not maintained. Organizations running affected kernel versions face significant risk as this vulnerability can be exploited by any local user with basic file system access, potentially leading to complete system compromise. The vulnerability's exploitation requires minimal privileges and can be automated, making it particularly attractive to malicious actors seeking persistent access to systems. The combination of setgid directory access with truncate/ftruncate operations creates a particularly dangerous attack surface that can be leveraged for both information gathering and privilege escalation purposes.
Mitigation strategies for CVE-2008-4210 require immediate kernel updates to versions 2.6.22 or later where the vulnerability has been patched. System administrators should prioritize patching affected systems, particularly those running older kernel versions that may be exposed to local privilege escalation attacks. Additional protective measures include monitoring for unauthorized file creation in setgid directories and implementing strict file system access controls. The kernel patch addresses the core issue by ensuring that setuid and setgid bits are properly stripped during write operations, preventing the privilege escalation vector. Organizations should also consider implementing additional security controls such as mandatory access controls, file integrity monitoring, and regular security assessments to detect potential exploitation attempts. The vulnerability highlights the importance of maintaining up-to-date system software and demonstrates how kernel-level security flaws can have far-reaching consequences for system integrity and data protection. Regular security audits and vulnerability management processes are essential to identify and remediate similar issues before they can be exploited by malicious actors.