Source: cve@mitre.org
Multiple race conditions in the handling of O_DIRECT in Linux kernel prior to version 2.4.22 could cause stale data to be returned from the disk when handling sparse files, or cause incorrect data to be returned when a file is truncated as it is being read, which might allow local users to obtain sensitive data that was originally owned by other users, a different vulnerability than CVE-2003-0018.
Critical vulnerability in older Linux kernels (pre-2.4.22) allows local users to read sensitive data due to race conditions when handling the O_DIRECT flag with sparse files. This flaw can lead to data leakage and compromise the confidentiality of user data, potentially exposing confidential information. This vulnerability is a significant risk for systems running outdated kernels.
Step 1: File Setup: A local user creates a sparse file and populates it with data, including sensitive information.
Step 2: Concurrent Operations: Two processes are initiated: one to read the file using O_DIRECT and another to truncate or modify the file.
Step 3: Race Condition Trigger: The read process begins reading data. Simultaneously, the other process truncates the file or modifies the data blocks. Due to the race condition, the read process might access stale or incorrect data.
Step 4: Data Leakage: The read process, due to the lack of proper synchronization, reads data that has been overwritten or is no longer valid, or incorrect data if the file is truncated during the read. This data may contain sensitive information from other users or previous versions of the file.
Step 5: Data Exfiltration (Optional): The malicious user then extracts the leaked data, potentially revealing confidential information.
The vulnerability stems from multiple race conditions within the Linux kernel's file system handling, specifically when dealing with the O_DIRECT flag and sparse files. The O_DIRECT flag bypasses the page cache, reading and writing directly to the disk. The core issue lies in the interaction between concurrent read and write operations on sparse files. When a file is truncated while being read with O_DIRECT, or when handling sparse file metadata, the kernel's synchronization mechanisms are insufficient. This leads to a stale data scenario where the read operation might access data that has been overwritten or is no longer valid, or incorrect data if the file is truncated during the read. The lack of proper locking and synchronization around the file's metadata and data blocks during these operations allows for these race conditions to occur. The specific functions involved in handling O_DIRECT reads and writes, along with sparse file metadata updates, are where the flaws reside. The root cause is a failure to properly serialize access to shared resources (file data and metadata) in a multi-threaded or multi-process environment.
While no specific APTs are directly linked to this specific CVE, the nature of the vulnerability (local privilege escalation) makes it a potential target for any attacker seeking to gain unauthorized access to a system. This vulnerability is not listed on the CISA KEV list due to its age and the availability of patches.
Monitor system logs for unusual file access patterns, especially involving O_DIRECT and file truncation operations.
Analyze file system metadata for inconsistencies, particularly in sparse files.
Implement file integrity monitoring to detect unauthorized modifications to sensitive files.
Review system calls related to file I/O, looking for suspicious combinations of open, read, write, truncate, and O_DIRECT flags.
Network monitoring for data exfiltration attempts after a potential exploitation.
Upgrade the Linux kernel to version 2.4.22 or later. This is the primary and most effective remediation.
If upgrading is not immediately possible, apply any available patches from the Linux distribution vendor.
Restrict access to sensitive files and directories.
Implement a robust file integrity monitoring solution to detect unauthorized modifications.
Regularly audit system logs for suspicious activity.