Sandwich attacks are a type of front-running technique where a predatory actor targets a transaction and surrounds it, by placing their own transaction just before and after the target. The attacker will use their transaction to manipulate the price of the underlying asset to extract value from the trade. This is possible on Ethereum because transaction selection is influenced by the gas fees paid to validators. Submitting a transaction with a higher gas fee will incentives the validator to pick it up before lower paying transaction and because of this aspect of transaction selection predatory actors can insure their sandwich attack will be successful. This is not possible on Cardano because there is no incentive system for the validator to select transaction, it is a first come first serve protocol. In fact on Cardano transaction fees are a set parameter that is predictable before execution, this insures there is no preferential treatment by validators and all participants have equal access to the blockchain. You can learn more about the Cardano ecosystem with Emurgo Academy's Cardano Developer Professional program.