External risk intelligence

Linux Kernel CIFS Session Reconnect Use-After-Free Vulnerability.

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2023-53794

The vulnerability exists in the Linux kernel CIFS (SMB) implementation related to session management. While SMB can be network-reachable, it is a file-sharing protocol typically restricted to internal networks or VPNs and is rarely exposed directly to the public internet in common, secure deployments.

Use After Free

Halo Surface Signal: 2 out of 5 — less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A critical security vulnerability has been identified in the Linux kernel's file sharing component that could allow for significant data compromise and system disruption. This issue stems from an improper handling of network session states, potentially leading to a use-after-free condition if not addressed. The main concern at this time is to confirm if our environment utilizes this specific file sharing technology and if it is exposed in a manner that could be targeted.

It’s a Linux kernel issue with network file sharing.
Affects session handling, potentially causing data issues.
Confirm relevance and exposure for our systems.

Attack Path

How an attacker could exploit the issue

An attacker could potentially trigger this vulnerability through network access to a system running a vulnerable Linux kernel. The issue lies within the CIFS (SMB) component, which handles file sharing. If an attacker can interact with this component under specific conditions related to session reconnection, it could lead to a use-after-free condition, potentially allowing for system compromise.

Network access to vulnerable system.
Triggering session reconnect logic.
Potential for full system compromise.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability in the Linux kernel's CIFS implementation could affect system stability and potentially allow for unauthorized access or modification of data when the system is handling network session reconnects. The issue stems from how the system manages exiting network sessions during a reconnect process, which, when exploited, could lead to unpredictable behavior and resource misuse.

Server session state.
Use-after-free during reconnect.
System instability and potential data access.

Operational Fix

Recommended remediation, mitigation, and detection steps

Given this vulnerability in the Linux kernel's CIFS (SMB) implementation, ownership likely resides with the infrastructure or platform teams responsible for managing the Linux environment, as well as potentially the network and security teams overseeing access controls to SMB services. The first practical step is to confirm the presence and reachability of the affected kernel component, determine its criticality to business operations, identify the accountable owner, and then plan remediation based on the assessed risk.

Infrastructure/Platform teams own remediation.
Verify SMB service reachability and criticality.
Coordinate with relevant teams for patching.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

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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 seamless data exchange between different systems, often serving as the foundation for SMB-based file shares in enterprise environments where Linux servers provide storage access to clients.

What does use-after-free mean for CVE-2023-53794?

A use-after-free is a memory management weakness where a program continues to use a pointer to a memory location after that memory has been freed or released. In this CVE, the flaw occurs during the CIFS session reconnection process; if the kernel tries to access a network session that is already in the process of being deleted, it creates a logic error that may lead to system instability or unpredictable behavior.

How is the CIFS session reconnect bug triggered?

The vulnerability is triggered during the server reconnection sequence within the CIFS component. It specifically involves the kernel incorrectly attempting to process or retain a session that is already marked for exit. Simply having an active connection is not enough; the error occurs when the system performs a reconnect operation while an existing session is in its final teardown stage.

How relevant is CVE-2023-53794 to my environment?

According to Halo Surface Signal, this vulnerability is categorized as 'Unlikely' to be directly reachable. While the CVSS score reflects a network-based vector, CIFS is a file-sharing protocol typically designed for internal network or VPN-restricted communication. It is rarely exposed directly to the public internet in secure, standard architectural deployments.

What should I do if my systems run CIFS?

First, verify if your Linux systems are running a kernel version that includes the affected CIFS component. Work with your platform or infrastructure teams to audit the reachability of your SMB services. Once you confirm the systems that utilize this technology, prioritize testing and applying the appropriate kernel updates provided by your distribution vendor to remediate the session management flaw.

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.