I see this post is old but, anyone notice the gibberish the bruteforce mode generates? ie: your SSID length is 3, yet MDK is on a roll with "dfhkxc24 &&#"
Well I have a small fix, below line 3448: (add the function on line 3449) add the following to mdk3.c,
memset(brute_ssid, '\0', 256);
load up wireshark, you will see your bruteforce now normalized and not filled with garbage, same for the output.