installing .NET Framework Sikkerhetsoppdatering (KB5087051) freezes at 27% done

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Method 1:

Temporarily turn off the Real-time protection on the Windows Defender app and try installing the update:-

That is, go to Settings > Privacy & Security > Windows Security > Virus & Threat Protection > Manage Settings.

Disable REAL TIME PROTECTION (and any other protections enabled). Try to install the update again. Once successful and after rebooting, re-enable the options you just disabled.

Method 2:

If you are still having issues, reset the Windows Update components by running these commands one by one in the Command Prompt (Administrator) window.

net stop wuauserv
net stop cryptsvc
net stop bits
net stop msiserver
ren C:\Windows\SoftwareDistribution SoftwareDistribution.old
ren C:\Windows\System32\catroot2 catroot2.old
net start wuauserv
net start cryptsvc
net start bits
net start msiserver

Then, restart your computer and install the updates.

Let me know if you still need more help.

For .NET Framework security updates that appear to freeze, the issue is often that the Native Image Generator (NGen.exe) is rebuilding the native image cache in the background. This can sit at a certain percentage (such as 27%) for many minutes while CPU usage is high, but it is still progressing.

To reduce the chance of it stalling for a very long time, run NGen manually before retrying the update:

1. Open an elevated Command Prompt (Run as administrator).
2. If the system is 64‑bit Windows (typical for an Asus Vivobook 15), run both commands:

      %windir%\microsoft.net\framework\v4.0.30319\ngen.exe update /force /queue
      %windir%\microsoft.net\framework64\v4.0.30319\ngen.exe update /force /queue
   

   On a 32‑bit system, run only:

      %windir%\microsoft.net\framework\v4.0.30319\ngen.exe update /force /queue
   

3. Wait for these commands to complete.
4. Restart the PC.
5. Run Windows Update again and install the .NET Framework Sikkerhetsoppdatering (KB5087051).

If the update still appears stuck, leave it running longer than usual (several tens of minutes) because native image regeneration can be very time‑consuming, especially if many .NET applications are installed.

If Windows Update in general reports failures with specific error codes (for example 0x80073701 or 0x800f0988), another supported mitigation is:

1. Open Command Prompt as administrator.
2. Run:

      dism /online /cleanup-image /startcomponentcleanup
   

3. Let it finish, restart the device, and then try Windows Update again.

References:

• Installing updates for the Microsoft .NET Framework 4 can take longer than expected in some scenarios
• When trying to install updates from Windows Update you might receive "Updates Failed. There were problems installing some updates, but we'll try again later" with Errors: 0x80073701, 0x800f0988