"Security Applications of Formal Language Theory" is a good overview. (If you don't have IEEE access, there's a tech report version.) Much of the work going on in this area has to do with characterizing classes of vulnerabilities in terms of unintended computational automata that arise from the composition of independent systems, often through novel vulnerability discovery motivated by considering the formal characteristics of a composed system and figuring out what can be wedged into the cracks. There's also been some interesting defensive work (Haskell implementation, an approach I'm interested in generalizing). That's probably a good start.

I have not actually learned Idris yet, and I think I could motivate myself better if I had a study partner; would you be interested in something like that?