There have been reports about the latest fix to Intel’s microcode to protect against the Spectre vulnerability causing higher than expected reboots and other unpredictable system behavior. So, in light of this, Intel has recommended users hold off on deploying the current fix while they continue testing.

Microsoft has offered an out of band update (KB4078130) that will disable this fix for the time being until a new, tested and stable update has been released. Currently, this Spectre variant has not been used in the wild for any attacks, so the current risk of disabling this patch is seen as fairly low.

Intel has reported issues with recently released microcode meant to address Spectre variant 2 (CVE 2017-5715 Branch Target Injection) – specifically Intel noted that this microcode can cause “higher than expected reboots and other unpredictable system behavior” and then noted that situations like this may result in “data loss or corruption.” Our own experience is that system instability can in some circumstances cause data loss or corruption. On January 22, Intel recommended that customers stop deploying the current microcode version on affected processors while they perform additional testing on the updated solution. We understand that Intel is continuing to investigate the potential effect of the current microcode version, and we encourage customers to review their guidance on an ongoing basis to inform their decisions.

While Intel tests, updates and deploys new microcode, we are making available an out-of-band update today, KB4078130, that specifically disables only the mitigation against CVE-2017-5715 – “Branch target injection vulnerability.” In our testing, this update has been found to prevent the described behavior in devices that have affected microcode. For the full list of affected devices, see Intel’s microcode revision guidance. This update covers Windows 7 (SP1), Windows 8.1, and all versions of Windows 10, for client and server. If you are running an affected device, this update can be applied by downloading it from the Microsoft Update Catalog website. Application of this payload specifically disables only the mitigation against CVE-2017-5715 – “Branch target injection vulnerability.”