receive_cross_chain_msg in both ChakraSettlement (Solidity) and settlement (Cairo) are missing access control and allow anyone, observing the mempool, to steal the signatures and frontrun the messages gas griefing the trusted entities that should call this function:
ChakraSettlement.sol
settlement.cairo
As we can see nowhere caller validation is done, only signatures are checked whether they belong to the current validators.
The grief is basically as ERC20 permit frontrunning, explained here. Although no harm is done, it affects the honest actors.
Add access-control allowing only Chakra trusted entities to call these functions.
