BSC ChainSwap Hack

The ChainSwap hack exploited a vulnerability in the smart contract that controlled the bridge's token mapping and minting functions. The technical root cause was an improper access control mechanism:

1. The attacker discovered a vulnerability in ChainSwap's token validation process
2. This allowed them to manipulate the verification function that checks whether tokens should be minted
3. By exploiting this flaw, they could mint arbitrary amounts of any token that was integrated with the bridge
4. The attacker then dumped these fraudulently minted tokens on decentralized exchanges

The vulnerability was in the verification system that authenticated cross-chain transactions:

// Simplified representation of the vulnerable verification function
function verifyTransaction(
    bytes memory signature,
    address token,
    address recipient,
    uint256 amount,
    uint256 nonce
) internal returns (bool) {
    // Rebuild the message that should have been signed
    bytes32 message = keccak256(
        abi.encodePacked(token, recipient, amount, nonce)
    );
    
    // Vulnerability: Insufficient validation of signatures
    // The verification didn't properly check that the signer was authorized
    address signer = recoverSigner(message, signature);
    
    // Only checked if signer exists in validator mapping, not role-based access
    return validators[signer];
}

The key issue was that the contract didn't properly validate the permissions of signers for specific token mint operations, allowing the attacker to craft transactions that appeared legitimate.