CVE-2009-0747 in Linux
Summary
by MITRE
The ext4_isize function in fs/ext4/ext4.h in the Linux kernel 2.6.27 before 2.6.27.19 and 2.6.28 before 2.6.28.7 uses the i_size_high structure member during operations on arbitrary types of files, which allows local users to cause a denial of service (CPU consumption and error-message flood) by attempting to mount a crafted ext4 filesystem.
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Analysis
by VulDB Data Team • 04/19/2025
The vulnerability described in CVE-2009-0747 represents a critical flaw in the Linux kernel's ext4 filesystem implementation that affects versions prior to 2.6.27.19 and 2.6.28.7. This issue resides within the ext4_isize function located in fs/ext4/ext4.h, which demonstrates improper handling of file size operations during filesystem mounting processes. The flaw specifically targets the i_size_high structure member, a component designed to handle large file sizes exceeding 32-bit limits, but the function fails to properly validate or restrict its usage during mount operations on arbitrary file types.
The technical nature of this vulnerability stems from the kernel's failure to properly sanitize input during filesystem mounting procedures. When a maliciously crafted ext4 filesystem is mounted, the ext4_isize function attempts to access the i_size_high member without adequate type checking or bounds validation. This improper access pattern creates a condition where the kernel enters an infinite loop or excessive CPU consumption pattern, effectively causing a denial of service scenario. The vulnerability operates at the kernel level, making it particularly dangerous as it can be exploited by local users without requiring elevated privileges, and the resulting system instability manifests through both CPU resource exhaustion and flooding of error messages that can overwhelm system logging capabilities.
The operational impact of this vulnerability extends beyond simple system unavailability, as it can lead to complete system lockups and make the affected system unusable for legitimate operations. Attackers can exploit this weakness by creating specially crafted ext4 filesystem images that trigger the problematic code path during mount operations, resulting in sustained high CPU utilization that prevents normal system functions from executing properly. The error message flooding aspect of the vulnerability compounds the issue by overwhelming system logs and potentially causing disk space exhaustion through log file growth, while simultaneously consuming additional system resources required to process and generate these error messages. This creates a cascading effect that can render the entire system unresponsive to legitimate user or system processes.
Mitigation strategies for CVE-2009-0747 should prioritize immediate kernel updates to versions 2.6.27.19 or 2.6.28.7, which contain the necessary patches to address the improper handling of the i_size_high structure member. System administrators should also implement filesystem validation procedures to prevent mounting of untrusted or unknown ext4 filesystems, particularly in environments where user-supplied storage media might be present. Additional protective measures include monitoring system resource utilization for unusual CPU consumption patterns and implementing log rotation policies to prevent disk space exhaustion from error message flooding. Organizations should also consider implementing network segmentation and access controls to limit the potential impact of local exploitation attempts. From a compliance standpoint, this vulnerability aligns with CWE-129 and CWE-362 categories, representing weaknesses in input validation and improper handling of resource consumption, while the exploitation techniques used would fall under ATT&CK tactics such as privilege escalation and denial of service through resource consumption.
The vulnerability demonstrates the critical importance of proper kernel-level input validation and resource management in operating system security. It highlights how seemingly minor flaws in filesystem handling code can result in significant system instability and availability issues. The issue also underscores the necessity of thorough testing and validation of filesystem operations, particularly when dealing with large file size handling and cross-platform compatibility considerations. Organizations should maintain robust patch management processes to ensure timely deployment of kernel security updates and implement comprehensive monitoring to detect unusual system behavior that might indicate exploitation attempts.