January 2026 security update failing with error 0x800f0991 - here's how to fix it.

The Problem

Windows 11's January 2026 cumulative update (KB5074109) is failing to install on builds 26200.7623 and 26100.7623 due to servicing stack inconsistencies. Common errors: 0x800f0991, 0x80073712, 0x800f0989.

Check for Corruption First

Run DISM health scan:

DISM /Online /Cleanup-Image /ScanHealth
DISM /Online /Cleanup-Image /RestoreHealth

Then verify system files:

SFC /scannow

Reboot and retry the update.

Reset Windows Update Components

Clear the update cache:

# Stop update services
Stop-Service -Name wuauserv, bits, cryptsvc -Force

# Rename update cache folders
Rename-Item -Path C:\Windows\SoftwareDistribution -NewName SoftwareDistribution.old -Force
Rename-Item -Path C:\Windows\System32\catroot2 -NewName catroot2.old -Force

# Restart services
Start-Service -Name wuauserv, bits, cryptsvc

Retry the update via Windows Update.

Run Windows Update Troubleshooter

# Launch troubleshooter
msdt.exe /id WindowsUpdateDiagnostic

Or navigate: Settings → System → Troubleshoot → Other troubleshooters → Windows Update → Run

Manual Install from Catalog

Download the .msu package directly:

  1. Visit Microsoft Update Catalog
  2. Select your Windows build (26200.7623 or 26100.7623)
  3. Download the .msu file
  4. Double-click to install

If manual install also fails with 0x800f0991, proceed to repair install.

Windows Repair Install (Most Reliable)

This method has the highest success rate:

Settings Method:
Settings → System → Recovery → Fix problems using Windows Update → Reinstall now

ISO Method:

  1. Download Windows 11 ISO
  2. Mount the ISO (double-click)
  3. Run setup.exe from mounted drive
  4. Choose "Keep personal files and apps"
  5. Follow prompts

This performs an in-place upgrade that fixes update components while preserving data.

Verify Success

# Check installed updates
Get-HotFix | Where-Object { $_.HotFixID -eq "KB5074109" }

# Check Windows version
winver

Expected build: 26200.7623 or 26100.7623

If Nothing Works

Microsoft has acknowledged this issue and is preparing an out-of-band fix. If all methods fail, you may need to wait for the official patch. Monitor Windows Health Dashboard for updates.