Commodore4Eva, which already released a working modified Xbox1 DVD firmware (coded instructions that are stored permanently in read-only memory) some weeks ago, released a new firmware for Xbox 360.
The release has already been tested by SniperKilla and Arakon and seems to be working fine, according to Xbox Scene.
The modified DVD firmware has been released exclusively for the Xbox 360 Toshiba-Samsung TS-H943 DVD-ROM drive. Just like Commodore4Eva's modified Xbox1 FW, it will also require raw/unmodified dumps (of same region as your console), some patching (security sector on ISO and DVD drive key on firmware) and DVD+DL double layers recordable discs in order to function.
"The package" also includes a second firmware that will enable the extraction of the security sector from an original disc with the TS-H943 drive connected to a PC.
All Xbox 360 executables (XEX containers files) are signed by Microsoft (with a private key only MS has). This means that if the user tries to change anything to the XEX file, the signature will be wrong and the file will not boot.
The Xtreme firmware for TS-H943 Xbox 360 is a backup firmware modification that can boot all game backups.
It features all Xtreme Xbox 360 backups, Xtreme Xbox 1 backups, Xbox 360 originals, and all Xbox 1 originals on Xbox 360, as the Xtreme0800 extraction firmware enables the drive to function natively under Windows without any hardware conversion/adaptors. Usage of Xbox Live is not recommended.
The new firmware can also read Xbox 360 security sector from PSN 04FB1F (Layer 0), Xbox 1 security sector from PSN 605FF (Layer 0), as the security sector must be extracted using Xtreme0800 360 firmware for Xbox360 games and Xbox 1 games. Unfortunately, the firmware is not able to boot Xbox 1 backups made with Xbox1 605b 0800 firmware.
More details here.