gistfile1.txt

(via http://forum.xda-developers.com/htc-one-m8/development/ota-3-28-401-6-t2899900)

1. Download the firmware, stock or no red text hboot
2. Boot your M8 into the bootloader, and check for fastboot usb mode
3. CMD: fastboot oem rebootRUU
4a. fastboot flash zip 4.16.401.9-Firmware.zip [for the stock one]
4b. fastboot flash zip 4.16.401.9-Firmware-noredtext.zip [for the noredtext one]
4c. fastboot flash zip 4.16.401.9-noredtext-HBOOT-only.zip [You need at least 4.16.401.9 Stock Firmware to flash this one!]
4d. You need to do the command twice if the CMD says: "pre-update, reflash immediately"
5. If you get "Successful" at the end of the CMD output, type: fastboot reboot-bootloader
6. Check HBOOT for 3.19, OS for 4.16.401.9
7. fastboot reboot
8. Done!

You need one of the following CIDs to flash:

modelid: 0P6B10000
cidnum: 11111111
cidnum: HTC__001
cidnum: HTC__J15
cidnum: HTC__E11
cidnum: HTC__102
cidnum: HTC__203
cidnum: HTC__405
cidnum: HTC__Y13
cidnum: HTC__304
cidnum: HTC__A07
cidnum: HTC__032
cidnum: HTC__M27
cidnum: HTC__K18
cidnum: HTC__016
cidnum: HTC__A48
cidnum: HTC__002