CVE-2009-0746 in Linux
Summary
by MITRE
The make_indexed_dir function in fs/ext4/namei.c in the Linux kernel 2.6.27 before 2.6.27.19 and 2.6.28 before 2.6.28.7 does not validate a certain rec_len field, which allows local users to cause a denial of service (OOPS) by attempting to mount a crafted ext4 filesystem.
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Analysis
by VulDB Data Team • 12/07/2024
The vulnerability described in CVE-2009-0746 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 make_indexed_dir function located in fs/ext4/namei.c, which handles directory creation operations in the ext4 filesystem. The flaw stems from inadequate validation of the rec_len field during filesystem mounting operations, creating a potential pathway for malicious exploitation that could result in system instability.
The technical nature of this vulnerability involves a missing input validation check for the rec_len field, which is a crucial component in ext4 filesystem directory entries. When a local user attempts to mount a specially crafted ext4 filesystem, the kernel's make_indexed_dir function fails to properly validate the rec_len field, leading to an out-of-bounds memory access condition. This validation failure results in a kernel oops condition, which is a kernel-level error that typically causes the system to crash or become unresponsive. The vulnerability specifically targets the filesystem mounting process where the kernel attempts to create indexed directory structures, making it particularly dangerous as it can be triggered during normal system operations.
The operational impact of this vulnerability extends beyond simple denial of service, as it provides local attackers with a method to destabilize systems running vulnerable kernel versions. Since the attack requires only local access to mount a crafted filesystem, it can be exploited by users with minimal privileges, making it particularly concerning for multi-user systems. The resulting kernel oops condition can lead to complete system crashes, requiring manual intervention to restore normal operations. This vulnerability affects the fundamental filesystem functionality and can potentially impact system availability, especially in environments where ext4 filesystems are commonly used for storage and data management.
Mitigation strategies for this vulnerability require immediate kernel updates to versions 2.6.27.19 or 2.6.28.7, which contain the necessary patches to validate the rec_len field properly. System administrators should prioritize patching affected systems, particularly those running older kernel versions that have not received security updates. Additionally, implementing proper filesystem validation procedures and monitoring for suspicious mounting attempts can help detect potential exploitation attempts. Organizations should also consider implementing network segmentation and access controls to limit local user privileges where possible, as this vulnerability can be exploited by users with basic system access. The fix addresses the underlying CWE-121 condition where insufficient validation of input data leads to memory corruption, aligning with the broader ATT&CK framework's approach to privilege escalation and system compromise through kernel-level vulnerabilities.