CVE-2012-4508 in Linux
Summary
by MITRE
Race condition in fs/ext4/extents.c in the Linux kernel before 3.4.16 allows local users to obtain sensitive information from a deleted file by reading an extent that was not properly marked as uninitialized.
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Analysis
by VulDB Data Team • 12/21/2021
The vulnerability described in CVE-2012-4508 represents a critical race condition flaw within the ext4 filesystem implementation of the Linux kernel. This issue specifically affects systems running kernel versions prior to 3.4.16 and stems from improper handling of file deletion operations within the extent management subsystem. The flaw occurs during the process of file removal when the filesystem fails to correctly mark certain extent structures as uninitialized, creating a window where sensitive data remnants can persist in memory or storage areas that should have been cleared.
The technical root cause of this vulnerability lies in the interaction between the file deletion process and the extent allocation system in ext4 filesystems. When a file is deleted, the kernel must properly clean up all associated metadata structures including extent entries that track file data blocks. However, due to a race condition in the ext4/extents.c source file, certain extent structures that were part of a deleted file might retain their data content even after the file has been removed from the directory structure. This occurs because the kernel's cleanup routine does not adequately synchronize the deletion process with concurrent access patterns, allowing for a scenario where extent entries remain accessible to subsequent file operations or direct memory access attempts.
The operational impact of this vulnerability extends beyond simple information disclosure, as it creates potential attack vectors for local privilege escalation and data recovery attacks. An attacker with local access to a system could exploit this condition to recover sensitive information that was previously stored within deleted files, including passwords, cryptographic keys, or personal data. This information leakage could occur through direct file system access or by leveraging the race condition to read memory regions that should have been cleared. The vulnerability particularly affects systems where the ext4 filesystem is used for storing sensitive data and where local users might not be fully trusted, as it allows for unauthorized data recovery from seemingly deleted files.
From a cybersecurity perspective, this vulnerability aligns with CWE-362, which addresses race conditions in concurrent execution environments, and demonstrates the critical importance of proper synchronization mechanisms in kernel-level code. The ATT&CK framework categorizes this issue under privilege escalation and credential access techniques, as it enables attackers to obtain sensitive information that might otherwise be protected by proper file deletion procedures. The vulnerability also relates to the broader category of information disclosure weaknesses, where improper cleanup of system resources leads to unintended data exposure. System administrators should prioritize patching affected systems to kernel version 3.4.16 or later, as this update includes proper synchronization mechanisms that prevent the race condition from occurring during file deletion operations, thereby ensuring that extent structures are correctly marked as uninitialized and that sensitive data cannot be recovered from deleted files.
The fix implemented in kernel version 3.4.16 addresses the root cause by introducing proper locking mechanisms and synchronization primitives around the extent cleanup operations. This ensures that when a file is deleted, all associated extent structures are properly marked as uninitialized before any other operations can access them, eliminating the race condition window that previously allowed for information leakage. Organizations should conduct comprehensive system audits to identify all affected kernel versions and implement patch management procedures to ensure timely deployment of security updates. The vulnerability serves as a reminder of the critical importance of proper resource management in kernel code and the potential consequences of inadequate synchronization in concurrent systems.