Technically speaking yes, though we are talking about a very obsolete exploit, you'd need a xenon or a zephyr, that has not been updated since 7371 if you have a (keyword) jtaggable xenon or zephyr you can downgrade it with your cpu key to 4532 (at the cost of efuses), flash cfw to the DVD drive and do the king Kong exploit, all this does is eject your DVD drive (with king Kong) and you had to insert a specifically made (burned) cd/dvd, which is where you stored homebrew. Really the softmod for the 360 would be the leaking of the private signing key like ps3 Tldr all 360 exploits rely on booting in some form of 4532 based kernel to run usigned code, the only reason homebrew existed is because of a extremely subtle flaw in programming that was introduced in this kernel and never again since appeared, rgh is the exploit that is the 'downgrade' everyone hoped for, it still uses the 4532 syscall exploit by allowing you to bypass your lockdown values. The 360 is specifically designed against softmodding from the cpu die up. This is how rgh works, rgh is the exploit that does exactly what we want, it allows you to bypass your lock down values, rgh still runs a modified 8955 dashboard that boots using the 4532 kernel iirc to use the syscall exploit. Due to how the hardware is designed on the 360 and the security structure, NO not possible, the only SOFTMOD was the King Kong or really the 4532 syscall exploit which required you to still have a flashed dvd drive, that was patched in dashboard 4552, they patched king Kong, but not the actual syscall exploit itself, they just patched you from accessing it through king Kong method, jtag was the the replacement to that issue (which is kinda both a soft and hard mod again due to how the hardware works) since the syscall exploit essentially is in the second stage bootloader (2bl) this was not updated from dashboard 2.4532.xx to 2.7371.xx, your dashboard version (CF lockdown) is signed using your console cpu key which is why you could downgrade between these dashes if you have the cpu key, once 8955 came out they updated the 2bl (8458) also has its own lock down counter, but this value is not signed using your cpu key, it uses Microsofts private key, and if we knew this key then jtag and rgh would be going around your ass to get to your elbow, so once they update the bootloader you cannot downgrade it, as this is the lowest version you would be able to downgrade to.

How to jailbreak xbox 360 without usb