Windows OS mitigations against CPU speculative execution vulnerabilities

Rackspace continues to evaluate and address a set of speculative execution vulnerabilities affecting certain central processing units (CPUs). You can find more information about the vulnerabilities in the following locations:

Spectre and Meltdown

Details related to the vulnerabilities can be found in:

Spectre and Meltdown variants 3A and 4 (May 21, 2018)

Details related to the vulnerabilities can be found in:

L1 Terminal Fault (L1TF) or Foreshadow (August 14, 2018)

Details related to the vulnerabilities can be found in:

It is important to note that the January 2018 Security Rollup Patch security patch, and other recent patches, have the capability to eliminate multiple possible vectors. However, for the patches to be fully functional, three additional registry keys must be implemented on each device, and the server must be rebooted for implementation. Rackspace is not pushing these keys because we have identified that devices might experience a performance impact or possible "blue screens" after these additional keys are implemented. Given this, we will not automatically install these keys unless customers opt-in to the remediation. We recommend that customers carefully consider the implications of applying the three additional registry keys and apply them as they deem appropriate. As a reminder, the main registry is required, and the patch must be installed for the additional keys to take effect.

Customers on managed colocation (colo) and Managed Infrastructure environments should reference the vendors for their recommended solutions to mitigate the vulnerability via patches of the operating system.

We recommend that those Microsoft Private Cloud customers running virtual machines on Hyper-V hypervisors follow Microsoft’s remediation guidance for customers who request host level patching. More info is available here: Protecting guest virtual machines from CVE-2017-5715 (branch target injection). We recommend that guest OS remediation align with the process noted in this document.

We have aligned with Microsoft guidance to patch your device and mitigate the vulnerability, and we will align with them on availability of the patches. Microsoft has released patches for all Windows operating systems. The following link provides access to currently available patches, as well as any necessary registry keys:

Note: The patches apply to only Windows operating systems. Additional patches for hardware and firmware for all platforms will be required and are continuing to roll out. We are working with our vendors to secure Unified Extensible Firmware Interface (UEFI) firmware and Basic Input/Output System (BIOS) updates. Timing of availability for updates will vary from vendor to vendor, adding another layer of complexity to full remediation. Firmware updates are the final part of the process to protect against Variant 2 2017-5715 of Spectre. Because it’s likely these updates will require reboots, customers must opt in to the maintenance prior to execution.

Important: Opting out of UEFI firmware updates and BIOS updates will result in not being protected against Variant 2 2017-5715 of Spectre.

Technical remediation

We have added new steps both for understanding and for those who want to fully remediate vulnerabilities.


Step 1: Install the update

  • The download and installation of the update will be dependent upon the device Windows Updates settings.
  • Check for updates to ensure the patch is available by going to the Windows Update control panel and checking for updates.

Note: Server 2008 requires the following registry key to be set:
“HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\QualityCompat” /v cadca5fe-87d3-4b96-b7fb-a231484277cc

Step 2: Enable update protection

There are three additional registry keys that must be configured to fully enable the protection capability of the update noted in Step 1. Instructions for enabling the mitigations are included in the "Enable mitigation" section.

Step 3: Apply OEM firmware

In addition to updating the registry, applying the update, and enabling update protection, an OEM firmware (processor microcode) update is required to enable the Branch target injection protection in the update.

Install patches

  1. Check for and install outstanding patches for the server.

  2. After the any outstanding patches have been install, reboot the server and ensure the latest Security rollups have been applied.

Enable mitigation

  1. Set the registry keys to enable the mitigation by running the following commands in the command prompt window on the local server:

    reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v FeatureSettingsOverride /t REG_DWORD /d 0 /f

    reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v FeatureSettingsOverrideMask /t REG_DWORD /d 3 /f

    reg add "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Virtualization" /v MinVmVersionForCpuBasedMitigations /t REG_SZ /d "1.0" /f

    Note: Branch Target Injection Mitigation will not be enabled until firmware updates have been applied.

Install the firmware updates

Instructions for applying firmware updates are outlined in Firmware/Microcode mitigations against CPU speculative execution vulnerabilities.

As always, please contact your support team if you have any questions.