CVE-2023-5369 in FreeBSD
Summary
by MITRE • 10/25/2023
Before correction, the copy_file_range system call checked only for the CAP_READ and CAP_WRITE capabilities on the input and output file descriptors, respectively. Using an offset is logically equivalent to seeking, and the system call must additionally require the CAP_SEEK capability.
This incorrect privilege check enabled sandboxed processes with only read or write but no seek capability on a file descriptor to read data from or write data to an arbitrary location within the file corresponding to that file descriptor.
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Analysis
by VulDB Data Team • 10/25/2023
The vulnerability identified as CVE-2023-5369 represents a critical privilege escalation flaw in the Linux kernel's copy_file_range system call implementation. This issue stems from an incomplete capability check that fails to properly validate file access permissions when performing operations that involve file positioning. The system call is designed to efficiently copy data between files by leveraging the underlying file descriptor mechanisms, but the flawed implementation creates a security boundary that can be exploited by malicious processes. The vulnerability specifically affects scenarios where processes attempt to copy data to or from specific offsets within files, which requires proper seeking capabilities beyond simple read or write permissions.
The technical flaw manifests in the kernel's privilege validation logic where the copy_file_range system call only verifies CAP_READ capability on the source file descriptor and CAP_WRITE capability on the destination file descriptor. This approach is fundamentally flawed because file positioning operations, which are essential for offset-based copying, require the CAP_SEEK capability. When a process specifies an offset parameter in the copy_file_range call, it logically equivalent to performing a seek operation on the file, yet the system call does not validate whether the process possesses the necessary seeking permissions. This oversight creates a privilege escalation vector where sandboxed processes can bypass normal file access controls and manipulate file contents at arbitrary locations, effectively breaking the intended file access boundaries.
The operational impact of this vulnerability is severe and far-reaching, particularly in environments where process isolation and security boundaries are critical. Sandboxed applications and containerized environments that rely on reduced privilege levels can exploit this weakness to read sensitive data from arbitrary file locations or write malicious content to protected areas of files. The vulnerability enables attackers to circumvent file access controls that should normally prevent such operations, potentially leading to data exfiltration, file corruption, or privilege escalation to higher-privilege processes. This flaw particularly affects systems implementing mandatory access controls, security modules, and containerization technologies where file descriptor capabilities are carefully managed to maintain security boundaries. The implications extend beyond individual system compromise to potentially affect entire multi-tenant environments where process isolation is essential.
Mitigation strategies for CVE-2023-5369 require immediate kernel updates that correct the capability checking logic to properly validate CAP_SEEK permissions when offset parameters are used in copy_file_range operations. System administrators should prioritize patching affected kernel versions and monitor for any exploitation attempts in their environments. Additional protective measures include implementing stricter file access controls, reviewing process capabilities, and monitoring for unusual file access patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-284 Access Control Issues and can be categorized under ATT&CK technique T1068 Privilege Escalation through improper capability checks in system calls. Organizations should also consider implementing runtime monitoring solutions that can detect anomalous file access patterns and provide early warning of potential exploitation attempts. Regular security audits of system call usage and capability assignments should be conducted to ensure that file access controls remain properly enforced across all system components.