Doom is said to be one of the first shooter games that came out on MS-DOS in 1993 and then pretty soon had their run on every platform as it was released for Nintendo, PlayStation in 1995 followed by a 2006 Xbox 360 addition, and then Doom was again relaunched in 2019 for the Xbox One, Nintendo Switch and PlayStation 4.
A custom save file from the developer KGSWS lets you execute an arbitrary code into the game's developer mode that lets you run Snake in The Ultimate Doom. The snake here is made up entirely of skulls (which is a form of texture that was available in-game) and you control the snake by steering it around the screen. After this exploit the modders have the question in mind that what more can be done here? Maybe run Pac-Man or Super Mario Bros in Doom?
Maybe so, actually. The fun part here isn't just the Snake, but the developer/modder KGSWS found an exploit by using the custom save files to run an arbitrary code within Doom that allows the user to tweak a lot of in-game details. Doom is said to be broken as there are wide amounts of ports of their source code though this is said to be a major one as it allows the user for more robust changes into the original DOS version of the file.
Look at that! An arbitrary code execution exploit has been found in original DOOM! (Ultimate DOOM 1.9 here) Check out this game of snake that gets enabled by loading a save game! #DOSGaminghttps://t.co/OYHXcd6X7G pic.twitter.com/RsA728a4RD— 𝔸𝕟𝕒𝕥𝕠𝕝𝕪 𝕊𝕙𝕒𝕤𝕙𝕜𝕚𝕟💾 (@dosnostalgic) March 24, 2021
Here's the GitHub link to the port to check it out for yourself, while there's also a tweet attached to see the port in action.