CVE-2003-0018 in Linux
Summary
by MITRE
Linux kernel 2.4.10 through 2.4.21-pre4 does not properly handle the O_DIRECT feature, which allows local attackers with write privileges to read portions of previously deleted files, or cause file system corruption.
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Analysis
by VulDB Data Team • 03/08/2021
The vulnerability described in CVE-2003-0018 represents a critical flaw in the Linux kernel's handling of the O_DIRECT file I/O feature within versions 2.4.10 through 2.4.21-pre4. This issue stems from improper management of direct I/O operations that bypass the kernel's page cache, creating a significant security weakness that can be exploited by locally authenticated users. The flaw specifically manifests when the kernel fails to properly invalidate or handle cached data structures associated with files that have been deleted or modified during direct I/O operations. This vulnerability falls under the broader category of improper handling of file system metadata and cache invalidation, which aligns with CWE-119 - Improper Access to Memory Location and CWE-200 - Information Exposure. The security implications extend beyond simple information disclosure, as the vulnerability can lead to file system corruption and unauthorized data access.
The technical mechanism behind this vulnerability involves the interaction between the O_DIRECT flag and the kernel's file system layer. When applications use O_DIRECT, they request I/O operations that skip the kernel's page cache entirely, directly accessing storage devices. However, in affected kernel versions, the kernel fails to properly synchronize or invalidate cached data structures that reference previously deleted files. This creates a scenario where data that should no longer be accessible remains in memory or cache locations, allowing local users with write privileges to read portions of data that had been deleted from the file system. The flaw particularly affects the ext2 and ext3 file systems, where the kernel's handling of direct I/O operations does not adequately account for the potential state changes in file metadata during concurrent operations.
The operational impact of this vulnerability is substantial for systems running affected kernel versions, as it provides local attackers with the ability to access data that should have been removed or made inaccessible through normal file system operations. This capability can lead to information disclosure of sensitive data, potentially including system configuration files, user credentials, or application data that had been deleted from the file system. The vulnerability also poses a risk of file system corruption, as the improper handling of cached data structures during direct I/O operations can result in inconsistent file system states. This type of attack vector aligns with ATT&CK technique T1005 - Data from Local System, where adversaries exploit local privileges to access restricted data. The vulnerability represents a privilege escalation path for local users, as they can leverage their write privileges to gain access to previously deleted content that may contain sensitive information.
Mitigation strategies for CVE-2003-0018 primarily involve upgrading to kernel versions 2.4.21-pre5 or later, where the O_DIRECT handling has been corrected to properly invalidate cached data structures and synchronize file system metadata. System administrators should also consider implementing additional security measures such as restricting write privileges to sensitive directories and monitoring for unusual file system access patterns. The vulnerability highlights the importance of proper cache invalidation procedures in kernel-level file system operations and demonstrates the need for thorough testing of I/O operations that bypass standard caching mechanisms. Organizations should also implement regular kernel updates and security patch management processes to address similar vulnerabilities in their systems, as this flaw represents a fundamental issue in how the kernel handles direct I/O operations and file system consistency. The fix implemented in subsequent kernel versions addresses the core issue by ensuring that cached data structures are properly invalidated when files are deleted or modified, preventing the exposure of previously deleted content through direct I/O operations.