CVE-2008-4554 in Linux
Summary
by MITRE
The do_splice_from function in fs/splice.c in the Linux kernel before 2.6.27 does not reject file descriptors that have the O_APPEND flag set, which allows local users to bypass append mode and make arbitrary changes to other locations in the file.
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Analysis
by VulDB Data Team • 08/20/2019
The vulnerability identified as CVE-2008-4554 represents a critical access control flaw within the Linux kernel's splice system call implementation. This issue resides in the do_splice_from function located in fs/splice.c, specifically affecting kernel versions prior to 2.6.27. The vulnerability stems from insufficient validation of file descriptor attributes during splice operations, creating a pathway for local privilege escalation and data integrity compromise. The flaw manifests when the kernel fails to properly validate whether a file descriptor has the O_APPEND flag set, which should normally prevent direct write operations to arbitrary file positions.
The technical implementation of this vulnerability exploits the splice system call mechanism which allows data to be transferred between file descriptors without requiring intermediate buffers in userspace. When a file descriptor with O_APPEND flag is used in a splice operation, the kernel should normally enforce append-only behavior, preventing writes to arbitrary offsets within the file. However, the do_splice_from function fails to check this flag, allowing malicious processes to bypass normal append mode restrictions. This creates a scenario where local users can manipulate file positions and write data at arbitrary locations within files, effectively circumventing the intended file access controls.
The operational impact of this vulnerability extends beyond simple data corruption, as it enables local attackers to manipulate file contents in ways that could compromise system integrity and security. An attacker with local access can leverage this flaw to modify critical system files, configuration data, or application resources without proper authorization. The vulnerability is particularly dangerous because it operates at the kernel level, making it difficult to detect and prevent through conventional userspace security measures. This type of flaw aligns with CWE-284 Access Control issues, specifically targeting improper access control mechanisms within kernel space operations.
From an adversarial perspective, this vulnerability maps to several ATT&CK techniques including privilege escalation through kernel exploits and persistence mechanisms. The ability to bypass O_APPEND restrictions creates opportunities for attackers to modify log files, system binaries, or configuration files, potentially establishing persistent backdoors or covering malicious activities. The vulnerability demonstrates how kernel-level flaws can be exploited to gain unauthorized access to file systems, making it a significant concern for system administrators and security professionals responsible for maintaining file integrity.
Mitigation strategies for CVE-2008-4554 require immediate kernel updates to versions 2.6.27 or later where the vulnerability has been patched. System administrators should also implement monitoring for unusual file access patterns and consider implementing additional file integrity monitoring solutions. The patch addresses the root cause by adding proper validation of file descriptor flags within the splice operation, ensuring that O_APPEND flag restrictions are properly enforced. Organizations should conduct comprehensive vulnerability assessments to identify systems running vulnerable kernel versions and prioritize patch deployment across all production environments. Additionally, implementing proper access controls and monitoring for unauthorized file modifications can help detect exploitation attempts even before the kernel is patched.