CVE-2006-0554 in Linux
Summary
by MITRE
Linux kernel 2.6 before 2.6.15.5 allows local users to obtain sensitive information via a crafted XFS ftruncate call, which may return stale data.
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Analysis
by VulDB Data Team • 07/22/2019
The vulnerability described in CVE-2006-0554 represents a significant information disclosure flaw within the Linux kernel's XFS filesystem implementation. This issue affects kernel versions prior to 2.6.15.5 and specifically targets the ftruncate system call functionality. The vulnerability arises from improper handling of file truncation operations that can lead to the exposure of previously deleted or overwritten data, creating a scenario where sensitive information may be inadvertently accessible to local users. The flaw exists at the intersection of filesystem management and memory handling, where the kernel fails to properly invalidate cached data structures during truncation operations.
The technical root cause of this vulnerability lies in the XFS filesystem's implementation of the ftruncate system call, which is used to change the size of a file. When a file is truncated, the kernel should ensure that any cached data associated with the truncated portions is properly invalidated and that no stale data remains accessible to subsequent operations. However, in affected kernel versions, the implementation fails to adequately manage the cache invalidation process, allowing previously allocated disk blocks to retain their data content even after the file has been truncated. This creates a situation where local users can potentially access data that should no longer be available, as the filesystem continues to return cached content from memory locations that were previously occupied by the file's data.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can potentially expose sensitive data that was previously stored in the truncated file's location. Attackers with local access to a system can exploit this flaw by creating a crafted XFS ftruncate call that triggers the return of stale data from memory caches. This could potentially reveal passwords, cryptographic keys, personal information, or other sensitive data that was previously stored in the same memory regions. The vulnerability is particularly concerning in multi-user environments where local privilege escalation or data leakage could occur, as it allows for the recovery of information that should have been permanently removed. The flaw affects the fundamental integrity of the filesystem's data management, potentially undermining the security assumptions that applications and users rely upon when performing file operations.
This vulnerability aligns with CWE-200, which describes improper output handling that can lead to information exposure, and represents a classic example of how cache management issues can create security vulnerabilities in operating system components. The ATT&CK framework categorizes this under privilege escalation and credential access techniques, as local users can leverage this flaw to gain unauthorized access to sensitive information. The exploitation of this vulnerability demonstrates the importance of proper cache invalidation and memory management in kernel-level filesystem implementations. Organizations should prioritize patching affected systems to address this vulnerability, as it represents a persistent risk that can be exploited by any local user with access to the system. The fix implemented in kernel version 2.6.15.5 involved correcting the cache invalidation logic during ftruncate operations, ensuring that memory blocks are properly cleared and that no stale data remains accessible after file truncation.
The broader implications of this vulnerability highlight the critical nature of filesystem security in operating system design and the potential for seemingly benign operations like file truncation to create security exposures. This flaw underscores the need for comprehensive testing and validation of filesystem operations, particularly those involving memory management and cache handling. System administrators should implement robust patch management procedures to ensure all systems are updated with the latest kernel versions that contain the necessary security fixes. The vulnerability also demonstrates the importance of understanding the underlying memory management mechanisms in operating systems, as improper handling of these low-level operations can create unexpected security risks that may not be immediately apparent during normal system operation.