CVE-2018-16871 in Linux
Summary
by MITRE
A flaw was found in the Linux kernel's NFS implementation, all versions 3.x and all versions 4.x up to 4.20. An attacker, who is able to mount an exported NFS filesystem, is able to trigger a null pointer dereference by using an invalid NFS sequence. This can panic the machine and deny access to the NFS server. Any outstanding disk writes to the NFS server will be lost.
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Analysis
by VulDB Data Team • 10/14/2024
The vulnerability identified as CVE-2018-16871 represents a critical null pointer dereference flaw within the Linux kernel's Network File System implementation across both NFSv3 and NFSv4 protocols. This issue affects all versions of the Linux kernel in the 3.x series and versions up to 4.20 of the 4.x series, making it a widespread concern for system administrators and security professionals managing networked file systems. The flaw manifests when an attacker successfully mounts an exported NFS filesystem and subsequently triggers an invalid NFS sequence, which causes the kernel to attempt to dereference a null pointer during processing. This type of vulnerability falls under CWE-476, which specifically addresses null pointer dereference conditions that can lead to system crashes and potential denial of service scenarios.
The operational impact of this vulnerability extends beyond simple system availability issues, as it can result in complete system panics and machine crashes that leave the affected system inaccessible. When the null pointer dereference occurs during NFS sequence processing, the kernel's response is to immediately crash the system, effectively denying access to the NFS server and rendering the machine inoperable until manual intervention occurs. This crash scenario is particularly concerning in production environments where continuous availability is critical, as it can lead to significant downtime and service disruption. The vulnerability also poses a risk of data loss, since any outstanding disk writes to the NFS server that were in progress at the time of the crash will be permanently lost, creating potential data integrity issues for systems relying on NFS for file storage operations.
From a security perspective, this vulnerability demonstrates how seemingly routine network file system operations can be exploited to create denial of service conditions that can have cascading effects throughout a network infrastructure. The attack vector requires minimal privileges since an attacker only needs to be able to mount an exported NFS filesystem, which typically requires network access and basic authentication credentials. This makes the vulnerability particularly dangerous in environments where NFS exports are configured with weak access controls or where attackers have legitimate network access to systems running NFS servers. The ATT&CK framework categorizes this type of vulnerability under privilege escalation and denial of service techniques, as it allows attackers to disrupt system operations without requiring elevated privileges. Organizations implementing NFS services should consider this vulnerability as part of their broader security posture assessment, particularly in environments where NFS is used for critical data storage and file sharing operations. The vulnerability also highlights the importance of kernel security updates and the need for regular patch management processes to ensure that systems remain protected against known exploits that can cause system instability and data loss.