Nlets Communication: Notice for Windows IIS Users and KB5066835

Important Notice: Potential IIS Disruption from Microsoft Update KB5066835

We’ve identified a critical issue affecting IIS web services running on unsecured ports following the installation of Microsoft Update KB5066835.

After applying this update, incoming requests may include a new header line: Upgrade-Insecure-Requests. This change can cause the IIS server to immediately reset the connection, preventing successful communication with your web services.

What We Found:

Multiple reports confirm similar disruptions across environments.
Removing KB5066835 and rebooting the affected system restores normal traffic flow.
More details are available in this Microsoft Answers thread.

Recommended Action:

Do not install KB5066835 in production environments without thorough testing.
Vet the update in a controlled test environment to ensure compatibility with your IIS configuration.
If already installed and experiencing issues, consider removing the update and rebooting as a temporary workaround.

We’re continuing to monitor the situation and will share updates as they become available. Please reach out to our support team if you need assistance.

If you are not running Microsoft IIS, you may disregard this message.