The Dangers of Backdoors in ERC20 Smart Contracts: A closer look at the SAND token contract ??????
Smart contracts on the Ethereum blockchain have revolutionized the way we think about decentralized applications, but with this innovation comes a new set of security concerns. One vulnerability that has been identified in smart contracts is the presence of “backdoors.” A backdoor is a hidden provision in the contract code that allows certain individuals to bypass security restrictions and perform actions that would not be allowed for regular users.
An example of a backdoor in a smart contract is the use of “super operators.” In the ERC20 SAND token contract code provided, a provision is made for super operators that can bypass certain restrictions on the transfer of tokens.
public
returns (bool success)
{
if (msg.sender != from && !_superOperators[msg.sender]) {
uint256 currentAllowance = _allowances[from][msg.sender];
if (currentAllowance != (2**256) - 1) {
// save gas when allowance is maximal by not reducing it (see https://github.com/ethereum/EIPs/issues/717)
require(currentAllowance >= amount, "Not enough funds allowed");
_allowances[from][msg.sender] = currentAllowance - amount;
}
}
_transfer(from, to, amount);
return true;
}
The code above shows a function for transferring a specified amount of SAND tokens using the ERC20 standard using the Solidity programming language. The function checks that the sender of the message (msg.sender) is either the address from which the SAND tokens are being transferred or an address designated as a “super operator” (_superOperators[msg.sender]). If the sender is not from and not a super operator, the function checks that the sender