The _fillQuote function does not validate the received amount of buy tokens against a minimum expected value. This allows attackers to perform sandwich attacks, front-running the transaction to manipulate the swap price, resulting in significant slippage and loss of funds. The current check only ensures the amount is non-zero, which is insufficient to prevent such attacks.

The allowanceTarget in SwapArgs is not validated, allowing a malicious user to set it to an arbitrary address. This could lead to the contract approving a malicious spender to transfer unlimited or large amounts of the sell token, resulting in theft of funds if the parent contract does not properly restrict allowanceTarget.

The amountOut is calculated as the total balance of the buy token after the swap, including any pre-existing balance in the contract. This leads to incorrect accounting, overreporting the actual tokens received from the swap, which could cause fund mismanagement or exploitation in dependent logic.

The contract does not validate exchangeProxy and allowanceTarget addresses beyond checking exchangeProxy is non-zero. An attacker can supply malicious addresses to steal approved tokens. For example, if allowanceTarget is set to a malicious contract and swapCallData triggers a token transfer, the contract’s tokens can be drained. This leads to loss of all approved tokens, as the external call executes arbitrary code with the contract’s funds.