Submitted by 0xRajeev, also found by cmichel and shw
The agreement between the user and the router seems to already happen off-chain because all the fields are required for the initial In variantTransactionData call already. A router could pretend to take on a users cross-chain transfer, the user sends their prepare transaction, locking up funds on the sending chain.
But then the router simply doesnt respond or responds with a prepare transaction of amount=0.
The users funds are then locked for the entire expiry time, whereas the router does not have to lock up anything as the amount is 0, even no gas if they simply dont respond. In this way, a router can bid on everything off-chain without a penalty, and take down everyone that accepts the bid.
Recommend that maybe there could be a penalty mechanism for non-responsive routers that agreed off-chain, slashing part of their added liquidity. Could also be that the bid signature already helps with this, but Im not sure how it works as the off-chain part is not part of the repo.
LayneHaber (Connext) acknowledged:
