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Anonymous Sun Aug 26 21:12:07 2018 No.10846298 [Reply] [Original]

DISCLAIMER: This is for educational purposes only. I am not responsible for anything that you choose to do with this information. I strongly recommend that you do not deploy a contract like this.

the eosio.token in EOS has an exploit where you can take user's ram and steal their resources. Exploit was discovered a little while ago but I just checked, and a tonne of exchanges (including binance) and dapps are still vulnerable to it.

im not going to do the exploit myself in case the feds catch me or some shit lol, but ill explain how it works, so if any other devs or blackhats want to have some fun and do it yourself, be my guest ;). Granted, you will probably have to be a little familiar with how eos smart contracts and the eos API works.

okay here is the original link explaining the exploit (right click, and click translate to english): https://mp.weixin.qq.com/s/OE7hxaXyrQ6Ssn-2c55GBA

here is how you can do it:

in a smart contract, there is an event listener function called "apply", it listens to any incoming events on the contract and then executes a handler. inside the handler you can reference other functions in your contract.

here is the apply function:
extern "C" {
/// The apply method implements the dispatch of events to this contract
void apply( uint64_t receiver, uint64_t code, uint64_t action ) {
if(action == N(transfer)) { //Here we make sure that the action is a `transfer` action from any contract that is or follows eosio.token standard
//Here is the handler for the event where we can put our exploit function
exploit_function(reciever);
}
}
}

before we go any further we have to include the currency.hpp file so that we can get a reference to the `transfer` struct and then get person who sent the action (it'll be more clear why we need this in a minute):
#include <eosiolib/currency.hpp> //This uses `currency` as a namespace.

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