Windows 8 build 8422 (fbl woa)

Windows 8 build 8422 (with a build tag of 8422.0.fbl_woa.120524-2000) is a post-Release Preview build of Windows 8. This build was leaked on 2019-02-19 only in the ARM architecture.

Getting the build to boot
Contrary to popular belief, this build is actually bootable, but it has only been tested on the Surface RT 1st generation. First you'll need to make a Windows RT 8.0 recovery drive, so the proper boot files can be added (mainly, a signed bootarm.efi). Next, you'll need to install the Secure Boot Debug Policy to your device. Enable test signing, mount the WIM, and follow the steps for registry and dll modifications. Commit your changes when done. To get the build to boot on the Surface RT, add HalExtTegra2.dll and NvHalExtDma.dll from build 9200 (RTM Windows RT 8.0) and add the following keys to the SYSTEM hive (mount the SYSTEM hive in a 9200 WinPE installation).

SYSTEM\ControlSet001\Control\OSExtensionDatabase\VEN_NVDA&DEV_0009

SYSTEM\ControlSet001\Control\OSExtensionDatabase\VEN_NVDA&DEV_000A

After adding those keys, add the following string values to the keys

HALExtension=NvHalExtDma.dll (0009)

HALExtension=HalExtTegra2.dll (000A)

After everything is done, make sure your BCD is enabled for test signing.

Without these modifications, the build will fail to boot with a 0x5C error.