selfdestruct-detect

EVM Selfdestruct Detection

Detect the possibility of a self-destruction happening during the execution of an Ethereum smart contract by determining whether the runtime bytecode ran by the Ethereum Virtual Machine contains a (possibly) reachable SELFDESTRUCT instruction.

Usage

npm i selfdestruct-detect

How does it work?

First of all, the application breaks down bytecode into its opcodes. Secondly, it loops over the opcodes, and skips over push data (if any). If it comes across a halting opcode (STOP, RETURN, REVERT, INVALID, SELFDESTRUCT), it will correctly assume all following opcodes are unreachable, until it can find a valid jump destination (JUMPDEST). While this method does prevent some false positives (like the metadata hash, included by the Solidity compiler), it will not detect whether code is unreachable due to exceptional halting, excluding halting due to the INVALID (0xfe) opcode.

Please note that this tool is unable to determine whether a contract will actually self destruct at any given time, it only detects whether it might be possible.

Why is this useful?

Ethereum's Constantinople fork introduces a new opcode called CREATE2, which allows contracts to deploy other contracts at address keccak256( 0xff ++ address ++ salt ++ keccak256(init_code))[12:] (instead of the usual keccak256(rlp([sender, nonce]))). Unfortunetaly, including keccak256(init_code) in the address formula does not prevent contracts from redeploying different code at the same address. For example, init_code could essentially just be "call contract x for runtime bytecode" which would allow for keccak256(initCode) to stay the same, even if contract x decides to return different runtime bytecode.

While there is no way to deploy code at an address which already exists in the state, contracts can remove themselves from the state by self-destructing (using the SELFDESTRUCT opcode), which would allow different code to be redeployed. Since (currently) there's no way of finding out whether a contract was deployed using CREATE2, a possible detection method for this attack vector would be to check whether the runtime bytecode contains a SELFDESTRUCT opcode. Interfaces which allow users to interact with Ethereum smart contracts can (and should!) implement this check to warn users when interacting with unstable smart contracts.

Read more: Potential security implications of CREATE2? (EIP-1014)

Example

Node.js

const { mightSelfdestruct } = require("selfdestruct-detect");
const Web3 = require('web3');
const web3 = new Web3(new Web3.providers.HttpProvider("https://api.mycryptoapi.com/eth"));
const CryptoKitties = "0x06012c8cf97BEaD5deAe237070F9587f8E7A266d";
 
web3.eth.getCode(CryptoKitties).then(code => {
    if(mightSelfdestruct(code)) {
        console.log("Warning: CryptoKitties contract possibly contains a self-destruct method!");
    } else {
        console.log("Success: CryptoKitties contract does not contain a reachable self-destruct instruction.");
    }
});

Browser

const { mightSelfdestruct } = window.SelfdestructDetect;
const web3 = new Web3(new Web3.providers.HttpProvider("https://api.mycryptoapi.com/eth"));
const DAI = "0x89d24A6b4CcB1B6fAA2625fE562bDD9a23260359";
 
web3.eth.getCode(DAI, function(err, code) {
    if(err) throw err;
    if(mightSelfdestruct(code)) {
        console.log("Warning: DAI contract possibly contains a self-destruct method!");
    } else {
        console.log("Success: DAI contract does not contain a reachable self-destruct instruction.");
    }
});

References

• EIP 1014: Skinny CREATE2
• Potential security implications of CREATE2? (EIP-1014)