After KB5079473 update, C: drive missing and system tools inaccessible

Problem summary

After installing Windows 11 update KB5079473, the C: drive became inaccessible for standard users and several system tools stopped opening correctly. Symptoms pointed to broken NTFS permissions and disabled inheritance on C: rather than a hardware or file‑system failure.​

Root cause

The update appears to have removed or corrupted NTFS inheritance and ACLs on the system drive (C:), so users lost permission to see or access files on C:, and some .msc tools (like Device Manager) failed with “Windows cannot access…” errors.

Fix you applied (step‑by‑step)

Use this as your “solution” text:

Open C: drive properties

In File Explorer, right‑click C: → Properties → Security tab.

  Click **Advanced**.
  
     Ensure **“Enable inheritance”** is turned on. If it is disabled, enable it so C: can inherit default system permissions again.
     
     **Temporarily grant access to everyone (to restore usability)**
     
        Still on the **Security** tab, click **Edit**.
        
           Add the **Everyone** principal and grant at least **Read & execute** (or temporarily Full control if needed to regain access and fix the ACLs).
           
              Apply the changes so users can see the contents of C: again while you repair the underlying permissions.
              
              **Optionally, normalize permissions from an elevated console** Run Command Prompt as Administrator and execute:
              
              ```dockerfile
              text
              takeown /F C:\ /R /D Y

icacls C:\ /reset /T /C /L icacls C:\ /grant Administrators:F /T /C ```

                 `takeown` restores ownership to Administrators recursively.
                 
                    `icacls /reset` restores default NTFS ACLs where possible.​
                    
                       The last command ensures the local Administrators group has full control on C:.
                       
                       **Reboot and validate**
                       
                          Restart the machine.
                          
                             Confirm that users can access **C:**, and that tools like **Device Manager**, **Control Panel**, and other `.msc` consoles open normally.
                             
                             **Mitigation for KB5079473**
                             
                                Uninstall **KB5079473** if the issue started right after this update, and hide/hold it using your patch management or Windows Update tools until Microsoft publishes an official fix or updated build.
                                

If the C drive disappeared, are you now able to get into Windows?

1

If you are able to get into Windows.

Please provide full details on the problems you now see, also with regards to the C drive if you open File Explorer, what happens if you try to access the C drive, please provide a screenshot of any error you may see.

2

If you are unable to get into Windows, are you able to uninstall that update form the recovery environment.

Start your PC, just as Windows attempts to load (spinning dots), press and hold Power Button for 5 - 10 seconds to perform a Hard Shut Down

Do this twice

On the third start Windows will boot into the Recovery Environment and from there you can access System Repair, Safe Mode, Command Prompt... etc.

The described behavior after a Windows security update indicates serious system corruption. Context does not provide specific guidance for KB5079473 or for a scenario where the C: system volume disappears and core tools become inaccessible, beyond general Windows Update troubleshooting and recovery patterns.

The only supported actions in context that are applicable are:

1. Use Windows Recovery Environment (WinRE) to repair or roll back
   • Force WinRE: power on the PC, as soon as the Windows or OEM logo appears, hold the power button to turn it off; repeat this 2–3 times until “Automatic Repair” appears.
   • In WinRE, try in order:
     • Troubleshoot → Advanced options → System Restore (if restore points exist).
     • Troubleshoot → Advanced options → Startup Repair.
     • If those fail, Troubleshoot → Reset this PC → Keep my files (this reinstalls Windows while preserving personal files but removes apps and settings).
2. If reset/repair from WinRE fails, perform a clean reinstall
   • From WinRE, use “Reset this PC → Remove everything” or boot from fresh installation media and reinstall Windows. This is destructive to apps and data on the Windows partition, so back up anything still accessible first.

Because the system drive is missing and tools are inaccessible, generic in‑Windows update troubleshooters and disk‑space checks from Settings are not applicable.

References:

• Troubleshoot problems updating Windows
• How to recover devices from an unbootable state after installing the January 2018 security update
• New partition appears after installing the Windows 10 April Update