Submitted by leastwood
The approve function has not been overridden and therefore uses xToken shares instead of the equivalent rebalanced amount, i.e. the underlying vault token amount.
The approved spender may spend more tokens than desired. In fact, the approved amount that can be transferred keeps growing as rewards continue to be distributed to the XTokenUpgradeable contract.
Many contracts also use the same amount for the approve call as for the amount they want to have transferred in a subsequent transferFrom call, and in this case, they approve an amount that is too large (as the approved shares amount yields a higher rebalanced amount).
The _allowances field should track the rebalanced amounts (i.e. the equivalent vault token amount) such that the approval value does not grow.
The transferFrom needs to be overridden and approvals should then be subtracted by the transferred vault token amount, not shares.
0xKiwi (NFTX) acknowledged, but disagreed with high severity and commented:
LSDan (judge) decreased severity to medium and commented:
