CVE-2001-0371 in FreeBSD
Summary
by MITRE
Race condition in the UFS and EXT2FS file systems in FreeBSD 4.2 and earlier, and possibly other operating systems, makes deleted data available to user processes before it is zeroed out, which allows a local user to access otherwise restricted information.
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Analysis
by VulDB Data Team • 02/13/2017
The vulnerability described in CVE-2001-0371 represents a critical race condition affecting Unix File System (UFS) and EXT2 File System implementations in FreeBSD versions 4.2 and earlier, with potential prevalence across other operating systems. This flaw occurs during the file deletion process when the system fails to properly synchronize the removal of file data with the zeroing out of that data before making it available for reuse. The race condition creates a temporal window where deleted file contents remain accessible to user processes, effectively undermining the fundamental security assumptions of file system protection mechanisms.
The technical implementation of this vulnerability stems from improper synchronization between the file system's metadata update operations and the actual data destruction processes. When a file is deleted, the file system first updates its directory entries and inode structures to mark the file as deleted, but the actual zeroing of the data blocks occurs asynchronously. During this brief interval between metadata update and data destruction, malicious user processes can access the still-available data through various means such as direct block access or by exploiting other file system interfaces. This behavior violates the principle of information flow control and creates a persistent data leakage channel that can be exploited by local attackers.
The operational impact of this vulnerability extends beyond simple information disclosure to encompass potential privilege escalation and data recovery attacks. Local users can exploit this condition to recover deleted files, access sensitive information from previously deleted files, or even reconstruct data that should have been permanently removed. The vulnerability affects the core file system integrity mechanisms, potentially allowing attackers to bypass access controls and recover confidential information that was thought to be securely deleted. This creates a significant risk for systems handling sensitive data where file deletion is expected to provide permanent data protection.
Security professionals should recognize this vulnerability as a classic example of a race condition that violates the principle of least privilege and data confidentiality. The issue aligns with CWE-362, which describes race conditions in security-sensitive operations, and can be mapped to ATT&CK technique T1070.004 for "File Deletion" and T1566 for "Phishing with Social Engineering" when combined with other attack vectors. The vulnerability demonstrates the critical importance of proper synchronization mechanisms in operating system components and highlights the need for rigorous security testing of file system operations. Mitigation strategies include upgrading to patched versions of FreeBSD 4.3 and later, implementing proper file system synchronization mechanisms, and conducting regular security audits of file system operations to identify similar race conditions in other system components.
This vulnerability underscores the fundamental challenge of maintaining data integrity in concurrent file system operations and serves as a reminder that even seemingly simple operations like file deletion can present complex security implications. The race condition affects not only the immediate data access but also the broader trust model of the operating system, potentially enabling attackers to reconstruct deleted data and compromise system confidentiality. Organizations should prioritize patching affected systems and implementing additional monitoring to detect unauthorized access to deleted file system data, particularly in environments where sensitive information processing is conducted.