10 March 2007


The more I beta-test/play/develop MMOs, the more I realize that developers still cut corners when it comes to security. If you're working on an MMO, especially before launch, it's very important to take a look at your game through the eyes of a hacker.

I've worked on hardening some games to the hacker types (and let's admit it: I was one myself once), so here's my short primer on MMOs and hacking:
  • Don't ship your game with the .PDB file! Obvious? Maybe, but not to some.
  • Turn off RTTI. Why are you using dynamic_cast anyways? It supports crazy things like casting horizontally in multiple inheritance. Not to mention that it's slow. Hackers love RTTI though, as it causes the executable to include mangled names of pretty much everything. If you need a dynamic typesafe casting solution, search the web or get a book. Or use virtual functions, though it's ugly as sin.
  • Take a look at your client in a hex editor, especially strings. You might be surprised at what you find. Those assert lines can actually contain a ton of useful information, like source file names and line numbers, not to mention C++ code itself. Or you might just find that you're including the class names of every message type in the game. Yes, it's been done.
  • Beware large areas of [un]initialized memory. Hackers love it when they already have space allocated in your program that they are free to write their code into. UO had a bunch of these before I cleaned them up, the largest of which being a 640x480 graphics buffer that was never fully used. Use the heap and make it lazy allocate. If possible, delete it as soon as you're done with it.
  • Change message IDs frequently. If you can do it right (and unpredictably), this can work well to foil those who like to read the network traffic.
  • Log stuff to the server, but don't take action on it right away. You don't want to do anything that lets a hacker know that you're onto them. Check with your legal department to find out what you can report, but it generally shouldn't be bad to do something like CRC the client in memory and send back a pass/fail response to the server. Or report if they're using a debugger, though this can be challenging. Unfortunately, uploading their modifications for review is anathema.
  • Watch your encryption keys. Yes, EQ2 actually held the encryption key in plaintext in a static buffer after negotiating it. It's fixed now, but hackers rejoiced!
  • Verify user data. UO has an immediate request/response targeting system. The server sends a request to the client with an ID which the client returns unmolested to the server. But what happens when a hacker figures out how to make use of changing that ID? You get the insurance bug.
  • Beware of unreleased/undocumented content. Again with UO, there were quite a few "gumps" that were in half-implemented features that still got pushed to live servers. A hacker figured out how to make use of one of these and ended up teleporting half the players on the server to a single X,Y location. Use source control branches or some configuration system to make sure this untested stuff can't be used. Period.
  • Don't make assumptions. You've heard the clich├ęs so i'll spare you. Just because a normal user can't see something (like a UI window or network message format) doesn't mean they can't exploit it.
  • Movement. A notoriously bad topic for MMOs, especially 3D ones, there should really be more seriousness here, at least in the way of logging. Servers can at least sanity check movement without having to run simulations of every client.
  • Buffer overruns/remote code execution. Yes, it can happen to you. Watch how you're using the string functions, especially the varargs ones (sprintf, sscanf, etc) and wide functions. The discussion on this one topic alone could be (and has been) a lecture in itself, so I'll just say: be aware of it.

  • You can never fully stop people from hacking on your game, but you can make it difficult (and you should). Then there's the other side of the coin: banning the people you catch hacking. Usually this is financially advantageous: if a hacker is turning people off of your game, it's probably not just one.

    Unfortunately, maintaining hack resistance and detection can be a full-time job, especially if your game is well established and there are many hack programs out for it. In such cases, it might be better to look at using something like PunkBuster.

    This is definitely an area of MMOs that should be collaborated on, since all MMO developers don't want the hackers :)

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