External risk intelligence

Linux Kernel CIFS Server Misaccounting Vulnerability

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2024-42256

This vulnerability exists within the Linux kernel CIFS (SMB) client implementation. It relates to internal filesystem subrequest retries and server connection management. This functionality operates at the kernel level for local filesystem operations and is not an internet-facing service, application, or network gateway.

Linux Kernel

6.10 to before 6.10.1

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 CIFS client could lead to misaccounting of server connections during specific file operations. While the issue is critical, its impact is confined to internal kernel processes related to file sharing protocols. The primary concern is confirming if this specific internal kernel behavior is relevant to your environment.

Mismanages server connections during file writes.
Important for understanding internal system behavior.
Confirm relevance and exposure to this kernel issue.

Attack Path

How an attacker could exploit the issue

An attacker could trigger a vulnerability in the Linux kernel's CIFS client by exploiting how it handles server connections during file write operations. When the system retries a subrequest, the code incorrectly manages server connections, leading to a state where critical counts are miscalculated. This misaccounting could potentially be leveraged to disrupt operations or cause system instability.

Requires network access to the affected system.
Triggers during specific file write operations.
Potential for data corruption or instability.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could affect the stability and integrity of the Linux kernel's CIFS client when handling subrequest retries, potentially leading to incorrect accounting of data transfer operations. This issue may occur under specific conditions involving retrying operations and server selection within the CIFS client, particularly when using multichannel mode with an Azure server.

Kernel filesystem operation integrity.
Misaccounting during subrequest retries.
System instability or data corruption.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability impacts the Linux kernel's CIFS client, specifically related to server selection during subrequest retries, which could lead to incorrect accounting of in-flight operations. Ownership likely resides with the infrastructure or platform teams managing the Linux systems, with initial triage focusing on identifying affected systems and assessing business criticality.

Identify affected Linux systems.
Verify exposure and business criticality.
Plan remediation during maintenance windows.

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 client?

The CIFS client is a core component within the Linux kernel that enables systems to mount and interact with network file shares using the SMB protocol. It allows Linux machines to read, write, and manage files stored on remote servers, such as those running Windows or Azure storage, by handling the low-level communication and data transfer tasks behind the scenes.

What does CVE-2024-42256 mean for system stability?

This CVE describes a logic error in how the kernel manages server connections during certain write operations. When a request fails and needs to be retried, the system may switch to a different server improperly, causing internal counters—specifically those tracking active operations—to become misaligned. This state of 'misaccounting' can lead to kernel warnings and potential system instability.

How is this CIFS vulnerability triggered?

The vulnerability is triggered during specific file write operations that encounter errors and require a retry. It specifically manifests when the CIFS client attempts to re-select a server for these subrequests. It is important to note that normal, successful write operations that do not require retries do not trigger this specific accounting error.

Do I need to worry about this vulnerability?

According to Halo Surface Signal, this issue is very unlikely to be a direct target for external actors. Because the vulnerability exists within the deep kernel-level management of filesystem connections rather than an internet-facing application or network service, it does not present a typical remote attack surface.

What are the first steps to address this kernel issue?

If you manage Linux systems, the first step is to identify machines running kernel versions within the 6.10 range that are affected. Since this is a kernel-level bug, remediation requires coordinating with your platform or infrastructure teams to plan for patching or updating the kernel during a 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.