CVE-2017-18216 in Linux
Summary
by MITRE
In fs/ocfs2/cluster/nodemanager.c in the Linux kernel before 4.15, local users can cause a denial of service (NULL pointer dereference and BUG) because a required mutex is not used.
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Analysis
by VulDB Data Team • 09/14/2025
The vulnerability identified as CVE-2017-18216 resides within the Linux kernel's ocfs2 filesystem implementation, specifically in the cluster nodemanager component located at fs/ocfs2/cluster/nodemanager.c. This flaw represents a critical denial of service vulnerability that affects systems running Linux kernel versions prior to 4.15. The issue manifests when local users can trigger a NULL pointer dereference and subsequent BUG condition through improper mutex usage. The ocfs2 filesystem is a distributed filesystem designed for high availability and shared storage environments, commonly used in enterprise and clustered computing scenarios where multiple nodes access the same storage resources simultaneously.
The technical root cause of this vulnerability stems from the absence of a required mutex lock mechanism during critical operations within the nodemanager subsystem. When multiple threads or processes attempt to access shared resources within the cluster management functionality, the lack of proper synchronization leads to race conditions where a mutex that should protect against concurrent access is omitted. This omission results in a scenario where a pointer that should be properly initialized becomes NULL, causing the kernel to attempt to dereference this null reference and subsequently trigger a BUG condition that terminates the kernel execution. The vulnerability operates at the kernel level and requires local user privileges to exploit, making it particularly concerning for systems where untrusted local users might have access to kernel-space operations.
The operational impact of CVE-2017-18216 extends beyond simple service disruption, as it can lead to complete system crashes and potential data loss in clustered environments. When exploited, the vulnerability causes the kernel to panic and reboot the affected system, resulting in denial of service for all services relying on the ocfs2 filesystem. This is particularly problematic in enterprise environments where high availability is critical, as cluster nodes may experience unexpected restarts that can disrupt ongoing operations and potentially lead to data inconsistency issues. The vulnerability affects systems where ocfs2 is actively used in cluster configurations, which are common in database servers, storage appliances, and enterprise computing infrastructures where shared storage is essential for maintaining service availability and data integrity.
Security professionals should address this vulnerability by upgrading to Linux kernel version 4.15 or later, which contains the necessary mutex synchronization fixes. Organizations using older kernel versions should implement immediate mitigations including disabling the ocfs2 filesystem if it is not actively required, restricting local user privileges on systems where the filesystem is present, and monitoring for potential exploitation attempts. The vulnerability maps to CWE-476 which describes NULL pointer dereference conditions, and aligns with ATT&CK technique T1499.004 for network denial of service attacks. Additionally, this vulnerability demonstrates the importance of proper synchronization mechanisms in kernel-space code and highlights the need for comprehensive testing of race conditions in distributed filesystem implementations. System administrators should also consider implementing intrusion detection systems to monitor for unusual kernel panic patterns that might indicate exploitation attempts, and maintain regular patching schedules to prevent similar vulnerabilities from being exploited in production environments.