executeFailedWithUpdatedArgs(...) shouldn't be able to change beneficiary

Description

When the ConnextRouter message fails, it records the message in the ConnextHandler and sends it the funds. In the ConnextHandler, it's possible to change the actions and arguments of a failed tx in executeFailedWithUpdatedArgs(...).

Thus, it's possible to change the beneficiary, which would leave room for attacks to steal assets.

Recommendation

Check the beneficiary of the first action to match the previous beneficiary.

Status

Acknowledged with the following statement: The issue identified is acknowledged by the Fuji team, however, as indicated the severity of this issue is low. The call to execute a failed transfer is permissioned and it's in the team's best interest to resolve failed transfers ethically.

During Q3-2023 the team will be working on general optimizations/improvements on the router contracts in which this fix will be implemented.