CVE-2015-8746 in Linux
Summary
by MITRE
fs/nfs/nfs4proc.c in the NFS client in the Linux kernel before 4.2.2 does not properly initialize memory for migration recovery operations, which allows remote NFS servers to cause a denial of service (NULL pointer dereference and panic) via crafted network traffic.
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Analysis
by VulDB Data Team • 07/02/2022
The vulnerability identified as CVE-2015-8746 resides within the Network File System version 4 implementation in the Linux kernel, specifically in the fs/nfs/nfs4proc.c file. This flaw represents a critical memory initialization issue that affects NFS client implementations across various Linux distributions prior to kernel version 4.2.2. The vulnerability manifests during migration recovery operations, which are essential components of NFSv4's failover mechanisms that allow clients to seamlessly transition between different server instances without disrupting file access operations. The improper memory initialization creates a condition where the kernel fails to properly set up data structures required for handling server migration scenarios, leading to a cascade of failures when malicious or misconfigured NFS servers attempt to exploit this weakness.
The technical exploitation of this vulnerability occurs through crafted network traffic sent by a remote NFS server that triggers the migration recovery path within the client's NFS implementation. When the NFS client encounters such traffic, it attempts to process migration recovery operations but fails due to uninitialized memory pointers that should have been properly allocated and configured. This results in a NULL pointer dereference, a classic symptom of improper memory management where the system attempts to access memory locations that have not been properly initialized. The consequence of this dereference is a kernel panic, which represents a severe system failure that terminates the operating system's ability to function properly and requires a complete system reboot to restore normal operations.
The operational impact of CVE-2015-8746 extends beyond simple denial of service to potentially compromise the stability and availability of systems relying on NFS for file storage operations. In enterprise environments where NFS is extensively used for shared storage, this vulnerability could be exploited by attackers to systematically disrupt services across multiple systems, particularly those running older kernel versions. The vulnerability aligns with CWE-457: Use of Uninitialized Variable, which specifically addresses the risks associated with variables that are not properly initialized before use. From an adversarial perspective, this vulnerability fits within the ATT&CK technique T1499.004: Endpoint Denial of Service, where adversaries target system resources to prevent legitimate use of services. The impact is particularly severe in environments where NFS is used for critical applications such as database storage, cluster file systems, or any service requiring persistent file access that cannot tolerate extended downtime.
Mitigation strategies for this vulnerability primarily focus on kernel version upgrades to 4.2.2 or later, which contain the necessary patches to properly initialize memory structures during migration recovery operations. System administrators should prioritize updating all NFS clients to patched kernel versions while also implementing network segmentation to limit exposure to untrusted NFS servers. Additional protective measures include monitoring network traffic for unusual patterns that might indicate exploitation attempts and configuring NFS client settings to minimize reliance on migration recovery features when dealing with untrusted network environments. The vulnerability serves as a reminder of the critical importance of proper memory initialization in kernel space operations and demonstrates how seemingly minor implementation flaws can result in catastrophic system failures, emphasizing the need for rigorous security testing and validation of kernel components that handle network protocols and system-level operations.