Symptoms

  • “Security Update for Windows (KB50xxxxx)” repeatedly fails with 0x80070643.
  • A .NET Framework update or repair ends with the same code.
  • The update reappears after every reboot.

What causes 0x80070643

  • The Windows Recovery Environment (WinRE) partition is too small for the update and has no room to grow.
  • A corrupt .NET Framework installation.
  • A pending reboot or a stuck installer service.

How to fix it

  1. For the WinRE update: disable ReAgentC, shrink the OS partition by ~250 MB, extend the recovery partition to about 750 MB, then re-enable ReAgentC (command below is the check/enable part; use Disk Management or diskpart for the resize).
  2. For .NET failures: download the offline .NET Framework Repair Tool and the latest runtime installer from Microsoft and reinstall.
  3. Reboot to clear any pending operations, then retry the update once.

Terminal / CLI command

reagentc /disable && reagentc /enable && reagentc /info

Elevated Command Prompt. Microsoft publishes an official PowerShell script for the KB5034441 partition resize — use it if you are unsure about manual diskpart steps.

How to confirm the fix: The update installs once and no longer returns in Windows Update.

Prevent it from coming back

Leave the recovery partition at its default size, and reboot before installing large updates.