Securing Windows Updates: MitM Risks & Protection

TL;DR

Windows Updates are vital for cyber security, but they can be targeted by attackers using ‘Man-in-the-Middle’ (MitM) attacks. This guide explains how to protect against this, focusing on verifying update sources and using secure connection methods.

Understanding the Risk

Windows Updates download files from Microsoft servers. An attacker could intercept this process, replacing legitimate updates with malicious ones. This is a MitM attack – they sit between your computer and the server, pretending to be both. This requires them to be on the same network as you (e.g., public Wi-Fi) or compromise your router.

How to Protect Your Windows Updates

1. Enable Secure Boot & TPM 2.0: These hardware features help ensure only trusted software loads during startup, making it harder for malware to interfere with the update process.
   • Check in your BIOS/UEFI settings.
2. Verify Update Sources (WSUS/MU): If you use Windows Server Update Services (WSUS) or Microsoft Update, ensure these servers are properly secured and only approve updates from official sources.
   • Regularly audit approved update lists.
   • Restrict access to WSUS/MU servers.
3. Use HTTPS: Windows Updates should always use HTTPS (secure HTTP). Modern versions of Windows do this by default, but it’s worth checking.
   • You can check the certificate used for updates in your browser when downloading updates directly.
4. Check Update File Hashes: Microsoft publishes SHA256 hashes for each update. You should verify that the downloaded file matches this hash.
   1. Download the correct hash value from the Microsoft Update Catalog website.
   2. Use PowerShell to calculate the hash of the downloaded update file:

      Get-FileHash -Algorithm SHA256 C:WindowsSoftwareDistributionDownload<update_filename>.msu

   3. Compare the calculated hash with the official Microsoft hash. If they don’t match, do not install the update!
5. Network Security: Protect your network.
   • Use a strong Wi-Fi password: Avoid easily guessable passwords.
   • Avoid public, unsecured Wi-Fi networks: These are prime targets for MitM attacks. If you must use them, use a VPN (Virtual Private Network).
   • Firewall: Ensure your firewall is enabled and configured correctly to block unauthorized access.
6. Keep Your Antivirus/Anti-Malware Up-to-Date: A good antivirus program can detect and prevent malicious updates from being installed.
7. Monitor Event Logs: Regularly check the Windows event logs for suspicious activity related to updates. Look for errors or unexpected events in the WindowsUpdate log.
   • Open Event Viewer (search for ‘Event Viewer’ in the Start menu).
   • Navigate to Applications and Services Logs > Microsoft > Windows > WindowsUpdate.

Advanced Protection: Certificate Pinning

Certificate pinning is a more advanced technique where you specifically trust only certain certificates from Microsoft. This makes it much harder for an attacker to spoof the update server, even if they have a valid certificate.

Implementing certificate pinning requires deeper technical knowledge and is typically done at the network level (e.g., using a proxy server or firewall rules). It’s not recommended for average users.