External risk intelligence

Linux Kernel cifs Use-After-Free Vulnerability.

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2023-53751

This vulnerability is located within the Linux kernel CIFS (Common Internet File System) client implementation. CIFS/SMB is typically used for internal network file sharing. It is not designed to be exposed directly to the public internet, and its deployment is restricted to local or internal private network environments.

Use After Free

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 vulnerability in the Linux kernel's file-sharing component could allow for serious security issues. This component is part of the system's core software, and while the main concern is confirming its relevance and exposure within your environment, a potential flaw at this level warrants attention.

Flaw in Linux kernel file-sharing code.
Widespread impact if present in your systems.
Confirm relevance and exposure for your environment.

Attack Path

How an attacker could exploit the issue

An attacker could potentially exploit a vulnerability in the Linux kernel's handling of network file sharing connections. By sending specially crafted network traffic, an attacker might be able to trigger a condition where the system attempts to use memory that has already been freed, leading to a crash or the execution of malicious code.

Requires network access.
Vulnerable component is updated.
Risk of system compromise.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could affect the integrity and availability of systems running the Linux kernel when using CIFS. Specifically, a use-after-free bug in the handling of server hostnames during reconnect operations could lead to unpredictable behavior or crashes. This could occur when the CIFS client attempts to re-establish a connection to a server.

System stability and data integrity.
When reconnecting to a CIFS server.
Crashes or unexpected service behavior.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability resides in the Linux kernel's CIFS client, a component typically used for internal file sharing rather than public-facing services. System owners should first confirm the presence and exposure of CIFS functionality within their environment. Identifying the accountable Linux system administrators or platform team is crucial for verifying potential reachability and business criticality before planning remediation, which may involve coordinating with vendors or applying updates during scheduled maintenance.

Linux administrators own the fix.
Verify CIFS usage and exposure.
Plan coordinated updates.

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?

CIFS, or Common Internet File System, is a protocol used by the Linux kernel to allow computers to share files and printers over a network. It enables a system to act as a client, connecting to and accessing remote file servers within a local or private network environment, which is a core function for many enterprise and server deployments.

How does the CVE-2023-53751 use-after-free bug work?

This is a memory management flaw. A use-after-free occurs when software continues to use a pointer to a memory location after that memory has been released. In this specific case, the Linux kernel improperly handles the hostname during CIFS reconnection processes, potentially allowing the system to reference cleared memory, which can lead to service instability or unauthorized code execution.

Can this vulnerability be triggered by any network activity?

No. The flaw is specifically tied to the CIFS client's reconnection logic. It is triggered when the kernel attempts to update or access server hostname information while a connection is being re-established. Normal, stable network operations that do not involve these specific reconnect sequences do not trigger the vulnerability.

How relevant is this issue for internet-facing systems?

According to Halo Surface Signal, this vulnerability is very unlikely to affect internet-facing systems. Because the CIFS protocol is designed for internal file sharing within private networks and is not meant to be exposed to the public internet, the practical risk of external exploitation is significantly lower than for web-facing services.

What are the first steps to address CVE-2023-53751?

Start by identifying systems in your infrastructure that utilize the CIFS client. Once you have an inventory, coordinate with your Linux administrators to verify if the affected kernel versions are in use. Because this is a core system component, remediation typically involves planning for vendor-provided updates or kernel patches during your next scheduled 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.