CVE-2006-4813 in Linux
Summary
by MITRE
The __block_prepare_write function in fs/buffer.c for Linux kernel 2.6.x before 2.6.13 does not properly clear buffers during certain error conditions, which allows local users to read portions of files that have been unlinked.
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Analysis
by VulDB Data Team • 04/24/2026
The vulnerability described in CVE-2006-4813 represents a critical file system security flaw affecting Linux kernel versions prior to 2.6.13. This issue resides within the __block_prepare_write function located in the fs/buffer.c file, which is a fundamental component of the kernel's buffer management system. The vulnerability stems from improper buffer clearing during error conditions, creating a scenario where deleted file contents remain accessible to local users through specific file system operations.
The technical implementation of this flaw involves the kernel's handling of buffer cache management when file operations encounter errors. During file deletion operations, particularly when unlinking files that are still open or being accessed, the __block_prepare_write function fails to properly clear memory buffers that should be invalidated. This occurs because the function does not adequately handle error paths where file system operations are interrupted or fail, leaving stale data in memory buffers that were previously associated with the deleted file content. The buffer clearing mechanism that should occur during these error conditions is either bypassed or incomplete, allowing data to persist in memory.
From an operational perspective, this vulnerability creates significant security implications for local users who can exploit the flaw to access portions of files that have been unlinked from the file system. The impact extends beyond simple data leakage as it allows attackers to potentially recover sensitive information that was previously deleted, including potentially confidential data, temporary files, or other sensitive content. This represents a violation of data confidentiality principles and can be exploited to gain unauthorized access to information that should no longer be available to users. The vulnerability affects any local user with access to the system, making it particularly concerning in multi-user environments where privilege separation is expected.
The flaw aligns with CWE-200, which addresses improper output handling, and relates to broader security principles around data sanitization and memory management in kernel space operations. From an attack perspective, this vulnerability maps to techniques described in the ATT&CK framework under persistence and privilege escalation tactics, as attackers can leverage this to access previously deleted data that may contain sensitive information. The vulnerability demonstrates poor memory management practices in kernel space and highlights the critical importance of proper buffer clearing during error conditions. System administrators should prioritize patching affected systems to prevent exploitation, as the vulnerability requires no special privileges beyond local access and can be exploited through standard file system operations. The fix implemented in kernel version 2.6.13 involved correcting the buffer clearing logic in the __block_prepare_write function to ensure that memory buffers are properly invalidated during error conditions, thereby preventing the leakage of deleted file content.