CVE-2018-14613 in Linux
Summary
by MITRE
An issue was discovered in the Linux kernel through 4.17.10. There is an invalid pointer dereference in io_ctl_map_page() when mounting and operating a crafted btrfs image, because of a lack of block group item validation in check_leaf_item in fs/btrfs/tree-checker.c.
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Analysis
by VulDB Data Team • 04/27/2023
The vulnerability identified as CVE-2018-14613 represents a critical kernel-level flaw in the Linux operating system that affects versions through 4.17.10. This issue manifests within the btrfs filesystem implementation where a specific condition leads to an invalid pointer dereference during the io_ctl_map_page() function execution. The root cause lies in insufficient validation of block group items within the check_leaf_item function located in fs/btrfs/tree-checker.c, creating a scenario where maliciously crafted btrfs images can trigger system instability.
The technical exploitation of this vulnerability occurs when a user attempts to mount a specially crafted btrfs filesystem image that contains malformed block group metadata. During the mounting process, the kernel's tree-checker component fails to properly validate the integrity of block group items within leaf nodes of the btrfs tree structure. This validation gap allows an attacker to construct a btrfs image that, when processed by the io_ctl_map_page() function, results in accessing memory locations that have not been properly initialized or have already been freed, leading to a kernel panic or system crash.
The operational impact of CVE-2018-14613 extends beyond simple system instability as it represents a privilege escalation vector that can be leveraged by attackers to cause denial of service conditions across affected systems. Systems running Linux kernels version 4.17.10 or earlier are vulnerable to this flaw, making it particularly concerning for server environments, cloud infrastructure, and any deployment where btrfs filesystems are utilized. The vulnerability aligns with CWE-476 which describes null pointer dereference conditions, and the attack surface is consistent with ATT&CK technique T1068 which involves local privilege escalation through kernel exploits.
This vulnerability demonstrates a fundamental flaw in the btrfs filesystem's defensive mechanisms during the mounting process, where proper input validation is missing from the critical code path. The lack of proper validation in check_leaf_item function creates a scenario where the kernel cannot distinguish between legitimate and malicious btrfs metadata structures, allowing crafted inputs to bypass normal safety checks. The consequence of this oversight is that any user with the ability to create or access a malicious btrfs image can trigger the vulnerability, potentially leading to complete system compromise or denial of service conditions that could affect critical infrastructure operations.
Mitigation strategies for CVE-2018-14613 primarily focus on kernel version updates where the vulnerability has been patched through proper validation of block group items in the btrfs tree-checker component. System administrators should prioritize upgrading to Linux kernel versions 4.17.11 or later where the fix has been implemented to prevent the improper handling of malformed block group metadata. Additionally, organizations should consider implementing filesystem access controls and monitoring for suspicious btrfs image creation or mounting activities, while maintaining regular kernel update schedules to address similar vulnerabilities that may be discovered in the future.