Deposits from L1 to L2 using L1CrossDomainMessenger will fail and will not be replayable when L2CrossDomainMessenger is paused

Summary

Deposits from L1 to L2 using L1CrossDomainMessenger will fail and will not be replayable when L2CrossDomainMessenger is paused.

Vulnerability Detail

Both L1CrossDomainMessenger and L2CrossDomainMessenger extend CrossDomainMessenger contract that can be paused.

When CrossDomainMessenger is paused then only relayMessage function will revert as it uses whenNotPaused modifier. It's still possible to call sendMessage when contract is paused.

In known issues section you can find following:

3.If the L1CrossDomainMessenger is paused, withdrawals sent to it will fail and not be replayable.

However there is another problem with pausing. In case if L2CrossDomainMessenger is paused and no matter if L1CrossDomainMessenger is pause or not(as sendMessage function is callable when contract is paused), then all deposits that are coming from L1 to L2 through the L1CrossDomainMessenger will fail on L2 side, as relayMessage will revert, because is paused. As result, it will be not possible for depositor to replay that deposit anymore as no information about the call is saved. All sent value will be minted to aliased L2CrossDomainMessenger address.

Example. 1.User wants to send himself some eth from L1 to L2 through L1CrossDomainMessenger. 2.When new TransactionDeposited event was fired by OptimismPortal, L2CrossDomainMessenger on L2 was paused for some reasons. 3.TransactionDeposited was explored by special service that sent tx to L2 node. 4.Sent value amount is minted to aliased L2CrossDomainMessenger address and L2CrossDomainMessenger.relayMessage is called which reverts. 5.Depositor lost his eth as he is not able to replay tx.

Impact

Lose of funds for depositor.

Code Snippet

https://github.com/sherlock-audit/2023-01-optimism/blob/main/optimism/packages/contracts-bedrock/contracts/universal/CrossDomainMessenger.sol#L212-L343

Tool used

Manual Review

Recommendation

Pause CrossDomainMessenger on both sides at same time(L1 and L2) and restrict call of sendMessage function when contract is paused.

sherlock-audit / 2023-01-optimism-judging

rvierdiiev - Deposits from L1 to L2 using L1CrossDomainMessenger will fail and will not be replayable when L2CrossDomainMessenger is paused #57