I don't think there are any bugs for it.
But that is only if you consider a "bug" as being something that does not require any external tool / 1337 hekkk / exploit or whatever you want to call it.
I don't think there is something that can't be done by hacking the shizzle out of s4 , you just need to be patient and know what you're doing .
There might be such tools , but if so, they're private :)