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An industry-wide, hardware-based security vulnerability was disclosed today. Keeping customers secure is always our top priority and we are taking active steps to ensure that no Azure customer is exposed to these vulnerabilities.

The majority of Azure infrastructure has already been updated to address this vulnerability. Some aspects of Azure are still being updated and require a reboot of some customer VMs for the security update to take effect.

You previously received a notification about Azure planned maintenance. With the public disclosure of the security vulnerability today, we have accelerated the planned maintenance timing and began automatically rebooting the remaining impacted VMs starting at PST on January 3, 2018. The self-service maintenance window that was available for some customers has now ended, in order to begin this accelerated update.

You can see the status of your VMs, and if the update completed, within the Azure Service Health Planned Maintenance Section in the Azure Portal.

During this update, we will maintain our SLA commitments of Availability Sets, VM Scale Sets, and Cloud Services. This reduces impact availability and only reboots a subset of your VMs at any given time. This ensures that any solution that follows Azure’s high availability guidance remains available to your customers and users. Operating system and data disks on your VM will be retained during this maintenance.

You should not experience noticeable performance impact with this update. We’ve worked to optimize the CPU and disk I/O path and are not seeing noticeable performance impact after the fix has been applied. A small set of customers may experience some networking performance impact. This can be addressed by turning on Azure Accelerated Networking (Windows, Linux), which is a free capability available to all Azure customers.

This Azure infrastructure update addresses the disclosed vulnerability at the hypervisor level and does not require an update to your Windows or Linux VM images. However, as always, you should continue to apply security best practices for your VM images.