loss of funds due to accidental transfer of ETH

[code423n4]

Lines of code

https://github.com/code-423n4/2022-06-connext/blob/b4532655071566b33c41eac46e75be29b4a381ed/contracts/contracts/core/promise/PromiseRouter.sol#L132

Vulnerability details

Issue: a relayer or other component can send ETH to PromiseRouter.sol by mistake.

Consequences: this will lead to loss of funds since there is no function to withdraw the ETH.

Affected Code

File: PromiseRouter.sol
131:   // ======== Receive =======
132:   receive() external payable {}

Recommended Mitigation Steps

Add a withdrawEth function, where onlyOwner can withdraw ETH that is not part of the fees.

[jakekidd]

Note: it may also be possible to simply remove the payable receive method here. Worth handling either way.

[LayneHaber]

Duplicate of #67

[0xleastwood]

Anyone can "accidentally" transfer ETH to a contract. Downgrading to QA.

[0xleastwood]

There is no path of exploit so this issue is really just a best practice.

[0xleastwood]

Merging with #263.