Does anyone see a vulnerability in this smart contract?

Question

blockchain

Hello. There is a solidity smart contract for Ethereum. Task: find a vulnerability.

contract SimpleToken{
    mapping(address => uint) public balances;
    
    /// Buy token at the price of 1ETH/token.
    function buyToken() payable {
        balances[msg.sender]+=msg.value / 1 ether;
    }
    
    /** 
     *  @dev Send token.
     *  @param _recipient The recipient.
     *  @param _amount The amount to send.
     */
    function sendToken(address _recipient, uint _amount) {
        require(balances[msg.sender]!=0); // You must have some tokens.
        
        balances[msg.sender]-=_amount;
        balances[_recipient]+=_amount;
    }
    
}

Thanks in advance

Answer 1

I would check like this: require(balances[msg.sender]>=_amount);
Because the sender, in theory, could send more than he has, if he has at least some coins.