- Ensure your Xbox Live account Login-Type is configured as "No barriers" aka. auto-login with no password prompt
- Set your console as "Home Console" for this account
- Download the App Game Script
- Start the app (to ensure license is downloaded/cached)
- Take your console offline! To make extra sure it cannot reach the internet, set a manual primary DNS address of 127.0.0.1
- Get a device/microcontroller that can simulate a Keyboard (rubber ducky or similar) - otherwise you have to type a lot manually
This method appears to use a UWP app called Game Script on the Xbox One to execute the code, and was discovered by a user named carrot_c4k3. It seems as though the hack will require a lot of manual typing, unless you have a device that can simulate a keyboard, according to the preparation instructions. Reportedly, the latest firmware update for the Xbox One has already patched the exploit out, with the last exploitable firmware being 10.0.25398.4478.
Source
Video guide on how to prepare your system
Proof of concept code