Issue since Security Update (KB5079473) (26200.8037)

Question

Can no longer access external hard drive or any files on it since Security Update (KB5079473) (26200.8037)

Answer 1

Hi Colin Dickie,
Welcome to Microsoft Q&A forum. I'm happy to help.

If you're certain KB5079473 has caused the issue, I have a workaround although it's not convenient to do so. It's performing an In-place upgrade.

Disclaimer: Let’s try performing an in-place install or in-place upgrade which will refresh your Windows files and operating system without removing files or applications. That being said, we always recommend that if you have important data, you should back it up before making large system changes. If you want to back up your data first, please do so. Once you are done backing up, you can follow the steps in the following guides: How to run In-place upgrade in Windows 11 - Microsoft Community

After performing an In-place upgrade, you will have 25H2 without recent updates. You may then choose to update the system to the moment before that KB or pause Windows Update and wait for future patches.

I hope that above information is helpful to you.

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Answer 2

1

Is your external drive a Samsung drive and if so, do you have any Samsung software installed on your PC?

2

Right click your Start Button and open Disk Management.

Expand the bottom pane so all drives are visible in that pane.

Please provide a screenshot of that Disk Management window.

Answer 3

The described symptom (external USB drive no longer accessible after a security update) matches known classes of issues where Windows updates affect USB storage handling or disk access permissions.

Based on the provided material, there are two relevant areas to check and remediate:

1. Confirm the USB storage device is correctly recognized and mountable
2. Check for permission or policy issues affecting removable/external media

1. Verify the USB storage device is recognized and mountable

On earlier Windows versions (Windows 7 / Windows Server 2008 R2), there is a documented issue where a USB storage device cannot be recognized or mounted, which is resolved by installing a specific update and rebooting. While the referenced article targets older systems, the troubleshooting pattern still applies: ensure the OS has fully applied the update and that a restart has occurred.

Actions:

1. Ensure the system has been restarted after Security Update KB5079473.
2. Disconnect the external drive, wait a few seconds, and reconnect it to a different USB port.
3. Open Disk Management and verify whether the drive appears and has a drive letter. If it appears without a letter, assign one.

If the drive is not recognized at all, this mirrors the “USB storage device cannot be recognized or mounted” scenario. In that documented case, the resolution is to apply the relevant hotfix/update and restart. For the current system, ensure all pending cumulative and driver updates are installed and that the system has completed all post‑update restarts.

2. Check for removable/external media permission or policy issues

The context also describes a scenario where NTFS disk access permissions for removable or external media can be affected, and how to determine whether a disk is treated as removable or external:

1. Open an elevated Command Prompt (Run as administrator).
2. Start PowerShell by typing:

      powershell
   

3. Run:

      Get-WmiObject -Class Win32_DiskDrive | Format-Table Name,Model,MediaType
   

4. In the output, locate the external drive and check the MediaType column:
   • If it shows Removable media or External hard disk media, it is treated as removable/external.

If the drive is listed as removable/external and access is blocked or inconsistent after the security update, the documented hardening guidance is:

• Enable BitLocker on the external drive to preserve OS‑level permissions and protect data.
• Or enable and configure controls for read/write access to removable devices or media via policy.

These measures ensure that disk‑level permissions are enforced correctly for removable/external media and can mitigate access issues introduced by security hardening.

If access remains blocked after confirming the drive is visible in Disk Management and the MediaType is correctly identified, consider:

• Temporarily connecting the drive to another Windows system to confirm the disk itself is healthy.
• Reviewing any removable‑media access policies that may have been tightened by the security update (for example, device installation restrictions or removable storage access policies) and adjusting them as needed.

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References:

• USB storage device cannot be recognized or mounted on a computer that is running Windows 7 or Windows Server 2008 R2
• NTFS disk access permissions for removable or external media could be bypassed