Check out ctf competitions. They have a number of "problems" of varying difficulties. Depending on the competition, the easier ones start out with simple stack

Check out ctf competitions. They have a number of "problems" of varying difficulties. Depending on the competition, the easier ones start out with simple stack buffer overflows, SQL injection, etc., and many competitors will post writeups after the competition. Ctftime.org is a good place for a list of competitions (note: some are more difficult, in that an unexperienced person won't be able to do the intro problems). I'd recommend checking out picoctf as a good intro one.