Welcome to Microcorruption tutorial and walkthrough. Microcorruption is an online, embedded debugger that starts from scratch and introduces the very foundations of memory corruption. It simulates (very well) the behavior of Texas Instruments’ MSP430 16-bit microcontroller. Personally I think Microcorruption is a very good ctf practice site overall, especially for beginners since it helps structuring low-level thinking, reading assembly language and getting used to low-level debugging.
All the levels below listed are explained in great detail for all of us to understand the underlying idea. These are not mere tutorials showing how to unlock the door but rather writeups explaining why the door is being unlocked.