Summary

When setting a new route, the new route allowance is set to type(uint256).max, however the old route allowance is kept at uint256.max as well. Because the approved address is an upgradable contract it would be wiser to reduce its allowance to 0 when moving on to a new router.

Vulnerability Details

As described above when setting a new router, the old router still has uint256.max this poses a threat as that current allowed contract is upgradable and if it becomes malicious there are no ways to reduce its current allowance.

Impact

In the scenario where a malicious upgrade is made, assets left on the contract can be siphoned away.

Tools Used

Manual review

Recommendations

Consider at least removing the allowance when moving to a new implementation.