On Namada, the validators are full nodes of Ethereum and their stake is also accounting for security of the bridge. If they carry out a forking attack on Namada to steal locked tokens of Ethereum their stake will be slashed on Namada. On the Ethereum side, there exists a limit to the amount of assets that can be locked to limit the damage a forking attack on Namada can do. To make an attack more cumbersome there also exists a limit on how fast wrapped Ethereum assets can be redeemed from Namada. This does not add more security, but rather makes the attack more inconvenient, and allows governance time to react.