The Standard

Summary

In the PoS model, proposers know well in advance if they will propose one or consecutive blocks ahead of time. In such a scenario, a malicious validator can hold back the transaction and execute it at a more favourable block number.

Vulnerability Details

Passing block.timestamp as the expiry/deadline of an operation does not mean "require immediate execution" - it means "whatever block this transaction appears in, I'm comfortable with that block's timestamp". Providing this value means that a malicious miner can hold the transaction for as long as they like (think the flashbots mempool for bundling transactions), which may be until they are able to cause the transaction to incur the maximum amount of slippage allowed by the slippage parameter, or until conditions become unfavorable enough that other orders, e.g. liquidations, are triggered.

Impact

This offers no protection as block.timestamp will have the value of whichever block the txn is inserted into, hence the txn can be held indefinitely by malicious validators.

Tools Used

Manual Review

Recommendations

Consider allowing function caller to specify swap deadline input parameter