External risk intelligence

Linux Kernel ksmbd Use-After-Free in SMB2 Tree Connect.

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2026-89788

This vulnerability affects ksmbd, the Linux kernel implementation of the SMB server protocol. SMB services are commonly exposed as file-sharing gateways or network storage endpoints, which are frequently reachable via the network in enterprise and consumer environments.

Use After Free

Halo Surface Signal: 4 out of 5 — likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A recently resolved vulnerability in the Linux kernel's ksmbd component could allow for system instability or unexpected behavior if exploited. This issue relates to how the system handles network connections for file sharing. While a fix is available, confirming the relevance and exposure of this specific component within your environment is the primary concern.

Connection handling flaw in Linux kernel.
Could impact system stability and file sharing.
Confirm relevance and exposure within your environment.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by sending specially crafted network requests to a system running the affected Linux kernel. This could occur when a new network share connection is being established, potentially leading to a system crash or allowing an attacker to gain unauthorized access.

Network exposure required.
Race condition during connection setup.
Kernel crash or potential unauthorized access.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability in the Linux kernel's SMB server implementation could allow an attacker to crash the system when a concurrent session logoff occurs during a tree connection. This could happen when the system is processing a request to connect to a shared resource over the network, and a user logs out of their session simultaneously.

Kernel crashes impacting system availability.
Use-after-free during network file sharing.
Denial of service for connected users.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability in the Linux kernel's ksmbd component likely requires attention from infrastructure or platform teams responsible for managing file-sharing services. The first practical step is to identify all Linux systems running ksmbd, determine their network exposure and business criticality, and locate the accountable system owners for remediation planning.

Infrastructure or platform teams own remediation.
Verify ksmbd network exposure and criticality.
Plan risk-based remediation actions.

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 ksmbd in the Linux kernel?

ksmbd is a kernel-level implementation of the SMB 3 server protocol. It allows Linux systems to act as high-performance file servers, enabling computers to share files, printers, and other resources across a network. It is typically found in environments requiring native, high-speed file storage capabilities.

What kind of vulnerability is CVE-2026-89788?

This is a use-after-free vulnerability, which is a type of memory corruption bug. It occurs when a program continues to use a pointer to a memory location after that memory has been freed. In this specific case, the kernel attempts to access a tree connection object that was already deleted by a concurrent session logout.

How can an attacker trigger this issue?

The vulnerability is triggered by a race condition during the establishment of a network share connection. An attacker must send specific network requests that coincide exactly with a session logoff. If no session logoff occurs simultaneously with a new tree connection attempt, the specific code path that leads to this memory error is not triggered.

Is my system at risk according to Halo Surface Signal?

Halo Surface Signal identifies this as a 'Likely' risk because ksmbd services are often configured as network-facing file storage endpoints. If your Linux server is exposed to the internet or reachable over an untrusted network, it has a higher potential for being reached by an attacker compared to a system restricted to an internal, private network.

What are the first steps to address this CVE?

First, identify which of your Linux systems have the ksmbd module active and enabled. Evaluate whether these systems are reachable over the network and determine the business impact if those services were to crash. Once you have an inventory, coordinate with your platform team to prioritize patching these specific servers.

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.