CVE-2018-13093 in Linux
Summary
by MITRE
An issue was discovered in fs/xfs/xfs_icache.c in the Linux kernel through 4.17.3. There is a NULL pointer dereference and panic in lookup_slow() on a NULL inode->i_ops pointer when doing pathwalks on a corrupted xfs image. This occurs because of a lack of proper validation that cached inodes are free during allocation.
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Analysis
by VulDB Data Team • 03/29/2023
The vulnerability described in CVE-2018-13093 represents a critical NULL pointer dereference flaw within the Linux kernel's XFS file system implementation that can lead to system crashes and potential denial of service conditions. This issue specifically affects kernel versions through 4.17.3 and manifests during pathwalk operations on corrupted XFS file system images, highlighting a fundamental weakness in the inode cache management subsystem.
The technical root cause of this vulnerability lies in the lookup_slow() function within fs/xfs/xfs_icache.c where the code fails to properly validate that inode->i_ops pointers are not NULL before attempting to dereference them. During pathwalk operations on corrupted XFS images, the system encounters cached inodes that have not been properly initialized or have become invalid during the allocation process. This improper validation creates a scenario where the kernel attempts to access memory locations through a NULL pointer reference, resulting in an immediate system panic and complete system crash.
The operational impact of this vulnerability extends beyond simple system instability as it can be exploited to cause persistent denial of service conditions on systems running affected kernel versions. When a corrupted XFS image is accessed through pathwalk operations, the system becomes immediately unstable and requires manual intervention to recover, potentially disrupting critical services and data access. This vulnerability affects systems where XFS file systems are in use, particularly those handling large volumes of data where corruption scenarios might occur due to hardware failures, improper shutdowns, or other system issues.
This flaw aligns with CWE-476 which describes NULL Pointer Dereference, a common class of software vulnerabilities that occur when a program attempts to access a memory location through a pointer that has not been properly initialized. The vulnerability also maps to ATT&CK technique T1499.004 which covers "File System Wipe" and related data destruction techniques, as the system crash can effectively render the file system inaccessible until manual intervention occurs. The improper validation of cached inodes during allocation represents a failure in proper resource management and memory safety practices that should be enforced throughout the kernel's file system subsystem.
The recommended mitigation strategy involves upgrading to kernel versions 4.17.4 or later where this vulnerability has been addressed through proper NULL pointer validation in the lookup_slow() function. System administrators should prioritize patching affected systems, particularly those running XFS file systems that may be subject to corruption scenarios. Additionally, implementing proper monitoring and alerting for system crashes or unexpected panics can help identify exploitation attempts or environmental conditions that may lead to this vulnerability being triggered. Organizations should also consider implementing redundant storage solutions and regular backup strategies to minimize the impact of such system instability on business operations.