CVE-2026-50381: Windows 10 21h2 Information Disclosure

CVE-2026-50381 Overview

CVE-2026-50381 is a type confusion vulnerability in the Microsoft Composite Image File System (CimFS) driver. An authenticated local attacker can exploit the flaw to disclose sensitive kernel or process memory. The issue is tracked under CWE-843: Access of Resource Using Incompatible Type.

The vulnerability affects multiple current Windows client and server editions, including Windows 10, Windows 11 (24H2, 25H2, 26H1), Windows Server 2022, and Windows Server 2025. Exploitation requires local access with low privileges and no user interaction. Microsoft published the advisory through the Microsoft Security Response Center.

Critical Impact
Successful exploitation allows an authorized local user to read confidential data from kernel memory, potentially exposing credentials, cryptographic material, or other sensitive artifacts loaded into privileged address space.

Affected Products

Microsoft Windows 10 21H2 and 22H2 (x86, x64, ARM64)
Microsoft Windows 11 24H2, 25H2, and 26H1 (x64, ARM64)
Microsoft Windows Server 2022 and Windows Server 2025

Discovery Timeline

2026-07-14 - CVE-2026-50381 published to NVD
2026-07-16 - Last updated in NVD database

Technical Details for CVE-2026-50381

Vulnerability Analysis

The flaw resides in the Composite Image File System (CimFS) driver, a Windows kernel component that mounts and services .cim container images. The driver interprets a resource as one data type when it was allocated or initialized as another. This type confusion causes the kernel to dereference structure fields at offsets that do not match the underlying object layout.

The result is an out-of-bounds read against adjacent kernel memory. An authenticated local attacker who invokes the vulnerable driver code path can retrieve data that should remain isolated from user mode. The confidentiality impact is high, while integrity and availability are unaffected.

Root Cause

Type confusion [CWE-843] arises when code fails to validate that a resource matches the expected type before use. In CimFS, the driver processes attacker-influenced metadata from a composite image and casts it to a structure that does not match the actual object shape. Subsequent field accesses read past intended bounds into adjacent kernel allocations.

Attack Vector

Exploitation requires local, authenticated access with low privileges. An attacker with the ability to mount or interact with a crafted CimFS image can trigger the vulnerable code path from user mode. No user interaction is required beyond the attacker's own actions. Microsoft has not reported active exploitation, and no public proof-of-concept is currently listed for this identifier.

For technical specifics on the affected code path, refer to the Microsoft Security Update Guide entry for CVE-2026-50381.

Detection Methods for CVE-2026-50381

Indicators of Compromise

Unexpected loading or interaction with cimfs.sys by non-administrative processes.
Creation, mounting, or access of unusual .cim composite image files in user-writable locations.
Repeated kernel-mode exceptions or bug checks referencing the CimFS driver in Setup or System event logs.

Detection Strategies

Monitor process creation events invoking CimFS APIs or cimdiskimage PowerShell cmdlets from unexpected users or paths.
Baseline legitimate CimFS usage in the environment; container and application virtualization workloads are common legitimate consumers.
Correlate anomalous CimFS activity with subsequent privilege-sensitive process reads or credential access behaviors.

Monitoring Recommendations

Enable and forward Windows Kernel-PnP and driver-loading telemetry to a centralized analytics platform.
Alert on new .cim file writes in temp directories or user profiles followed by mount operations.
Track patch compliance for the July 2026 Windows security updates across all endpoints and servers.

How to Mitigate CVE-2026-50381

Immediate Actions Required

Apply the July 2026 Microsoft security updates to all affected Windows 10, Windows 11, Windows Server 2022, and Windows Server 2025 systems.
Prioritize patching on multi-user systems, terminal servers, and shared workstations where local attackers are most likely.
Audit endpoints for unexpected CimFS usage and restrict interactive logon rights where feasible.

Patch Information

Microsoft has published fixes through the Microsoft Security Update Guide for CVE-2026-50381. Install the cumulative update corresponding to each affected Windows build. No supported configuration is exempt from patching, and no alternative long-term mitigation is provided by the vendor.

Workarounds

No official workaround is documented by Microsoft; installing the security update is the required remediation.
Restrict local logon and reduce standard-user counts on sensitive hosts to limit the attacker population until patches are deployed.
Where CimFS is not required, evaluate application allowlisting policies that block unauthorized processes from invoking the driver.

bash

# Verify patch deployment status on Windows using PowerShell
Get-HotFix | Sort-Object -Property InstalledOn -Descending | Select-Object -First 10

# Query WSUS/SCCM or Microsoft Update for compliance against CVE-2026-50381
Get-WindowsUpdateLog