CVE-2002-0572 in FreeBSD
Summary
by MITRE
FreeBSD 4.5 and earlier, and possibly other BSD-based operating systems, allows local users to write to or read from restricted files by closing the file descriptors 0 (standard input), 1 (standard output), or 2 (standard error), which may then be reused by a called setuid process that intended to perform I/O on normal files.
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Analysis
by VulDB Data Team • 01/21/2025
This vulnerability exists in FreeBSD versions 4.5 and earlier, as well as potentially other BSD-based operating systems, representing a significant security flaw that exploits the handling of file descriptors in setuid processes. The issue stems from the improper management of standard input output and error file descriptors during process execution, where local users can manipulate the system's file descriptor table to gain unauthorized access to restricted files. When file descriptors 0, 1, or 2 are closed by a user process, these descriptors become available for reuse by subsequent setuid programs that expect to perform normal I/O operations on standard streams. This creates a race condition and privilege escalation opportunity where malicious users can effectively redirect I/O operations to arbitrary files, bypassing normal access controls that should restrict such operations to authorized users only.
The technical flaw manifests when a setuid program opens a file or performs I/O operations without properly validating or reinitializing file descriptors that were previously closed by the calling process. This behavior violates fundamental security principles regarding process isolation and privilege separation, as the setuid program inherits the file descriptor state from its parent process. The vulnerability is classified under CWE-276, which addresses improper file permissions and access control, and aligns with ATT&CK technique T1548.1, which covers privilege escalation through setuid binaries. When a setuid process executes, it typically expects to have standard file descriptors open for normal operation, but if these have been closed or manipulated by the parent process, the setuid program may inadvertently perform I/O operations on files that the user should not be able to access, leading to information disclosure or file corruption.
The operational impact of this vulnerability is substantial, as it allows local users to bypass access controls and potentially read sensitive system files, write to restricted directories, or modify critical system components. Attackers can exploit this by first closing standard file descriptors and then executing setuid programs that will reuse these closed descriptors for file operations. This creates a persistent security risk since any setuid binary on the system could be targeted, including system utilities, network services, or administrative tools. The vulnerability is particularly dangerous because it operates at the kernel level where file descriptor management occurs, making it difficult to detect through standard application-level monitoring and potentially allowing attackers to maintain persistent access to restricted resources without triggering typical security alerts.
Mitigation strategies for this vulnerability require immediate system updates to patched versions of FreeBSD and other affected BSD-based systems, as this issue was addressed through proper file descriptor handling in kernel implementations. System administrators should also implement comprehensive monitoring of setuid binary execution and file descriptor operations, particularly focusing on processes that may be subject to manipulation of standard streams. The recommended approach includes ensuring that setuid programs properly initialize their file descriptor state before performing I/O operations, which aligns with security best practices outlined in the Secure Coding guidelines. Additionally, organizations should conduct regular security audits to identify and remediate similar issues in other system components, and implement proper privilege separation mechanisms that prevent user processes from manipulating critical system file descriptors. This vulnerability demonstrates the importance of proper file descriptor management in security-critical systems and reinforces the need for robust input validation and resource handling in kernel-level operations.