August Windows patch breaks some dual-boot systems: how to fix

The August security update for Windows patched a number of key vulnerabilities, but one of those patches seems to have caused problems for a number of users who use Linux and Windows on the same hardware. The issue mainly affects systems that use the GRUB 2 bootloader, one that's packed in with many Linux distributions, alongside Secure Boot. Thankfully, the problem can be fixed with little difficulty.

One of the security fixes packed into the update is meant to block older bootloaders that Microsoft deems as "vulnerable" from being used with Secure Boot. The workaround that made that possible in the first place is essentially an artificial signing process, and it's patched by way of a Secure Boot Advanced Targeting setting, or SBAT for short. The SBAT fix was not supposed to roll out to systems where the updater detected dual-boot setups, but something went wrong, and many such systems were affected. 

Users reportedly tried to fix this a number of ways, including directly deleting the SBAT setting, but to no avail. Those who dual-boot and have not yet taken the update are encouraged to hold off on it, and can use a special registry entry to opt-out of the current update cycle while Microsoft and their Linux partners work on a fix. 

Those who have already taken the update and been locked out of their dual-booting system can simply disable Secure Boot in the BIOS, then reinstall their Linux version of choice, and re-enable Secure Boot. Doing so will put the walls down, so to speak, and allow a full reinstallation of the bootloader that had been rendered useless by the patch. 

Not all dual-booters seem to have been affected. Those using more modern Linux versions, those who keep Windows and Linux on separate physical drives, and those who set up a Secure Boot control module with their own custom keys are among those reporting that the update did them no harm.