External risk intelligence

Linux Kernel CIFS Race Condition Vulnerability

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2023-54258

This vulnerability exists within the Linux kernel CIFS (SMB) filesystem client implementation. It is triggered during local kernel-level operations involving file handle management and oplock breaks. It is not a network service listening for public traffic; rather, it is a local component used by the system to access remote file shares, making it inaccessible from the public internet.

Halo Surface Signal: 1 out of 5 — much less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A recent vulnerability was identified in the Linux kernel's file-sharing component, specifically impacting how it handles certain file operations. While the issue has been resolved in updated versions, its potential impact underscores the importance of maintaining the integrity of core operating system components. The main concern is confirming relevance and exposure.

A technical flaw exists in Linux file sharing.
It impacts core operating system functionality.
Verify if your systems are potentially affected.

Attack Path

How an attacker could exploit the issue

An attacker could trigger this vulnerability by exploiting a race condition during file operations on a CIFS (SMB) network share. This occurs when the system is trying to close a file handle simultaneously with breaking an oplock (opportunistic lock), potentially leading to a system crash. The vulnerability lies in how the kernel handles these concurrent operations, specifically when checking for valid session information before responding to an oplock break.

Requires local access to the system.
Triggered by a race condition during file closing and oplock breaks.
Can lead to a denial-of-service (system crash).

Live Threat

Current exploitation, exposure, and threat context

A race condition in the Linux kernel's CIFS client could lead to system instability or a crash. This occurs when file operations, specifically closing files and handling oplock breaks, conflict during system unmount operations. The vulnerability is triggered by specific sequences of internal kernel events rather than direct external interaction.

System stability could be affected.
A race condition during file operations could occur.
The system may experience an "oops" or crash.

Operational Fix

Recommended remediation, mitigation, and detection steps

The Linux kernel's CIFS implementation is impacted by this vulnerability. Responsibility for addressing this likely falls to the infrastructure or platform teams managing the Linux systems, in coordination with security teams for risk assessment. The first practical step is to identify all Linux systems utilizing the CIFS client, assess their exposure, and determine business criticality before planning remediation.

Infrastructure/platform teams own remediation.
Verify CIFS client usage and system criticality.
Plan updates during a maintenance window.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is the Linux kernel CIFS component?

The CIFS (Common Internet File System) component in the Linux kernel is the client-side implementation that allows a Linux system to access and mount remote file shares, such as those hosted on Windows servers or NAS devices. It enables users and applications to interact with remote files as if they were stored on a local drive.

What is the nature of the CVE-2023-54258 vulnerability?

This vulnerability is a race condition. It occurs when two internal kernel processes—closing a file handle and responding to an oplock (opportunistic lock) break—happen simultaneously in an conflicting order. This conflict can lead to a kernel oops, which is a state where the kernel detects a problem it cannot resolve, typically resulting in a system crash.

How is this race condition triggered?

The flaw is triggered by specific timing during file operations on a CIFS mount, particularly when an unmount operation occurs at the exact moment a lease break is being processed. Because it depends on the precise sequence of these internal system events, it is not triggered by simple or routine network access to a file share.

Is my system exposed to this CIFS vulnerability?

According to Halo Surface Signal, this vulnerability is very unlikely to be exploited from the internet. The issue resides within the local kernel-level code that manages file handle states. It is not an exposed network service listening for public connections, which significantly reduces the risk profile for standard deployments.

What are the first steps to address this issue?

The primary step is to identify all Linux systems in your environment that actively use the CIFS client to mount remote file shares. Once identified, evaluate the criticality of these systems and coordinate with your infrastructure team to schedule standard kernel updates or security patches during your next regular maintenance window.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.