Submitted by cmichel, also found by WatchPug
A single QuickAccount can serve as the privilege for multiple identities, see the comment in QuickAccManager.sol:
If there exist two different identities that both share the same QuickAccount (identity1.privileges(address(this)) == identity2.privileges(address(this)) == accHash) the following attack is possible in QuickAccManager.send:
Upon observing a valid send on the first identity, the same transactions can be replayed on the second identity by an attacker calling send with the same arguments and just changing the identity to the second identity.
This is because the identity is not part of the hash. Including the nonce of the identity in the hash is not enough.
Two fresh identities will both take on nonces on zero and lead to the same hash.
Transactions on one identity can be replayed on another one if it uses the same QuickAccount.
For example, a transaction paying a contractor can be replayed by the contract on the second identity earning the payment twice.
This issue of using the wrong nonce (on the identity which means the nonces repeat per identity) and not including identity address leads to other attacks throughout the QuickAccManager:
Ivshti (Ambire) confirmed:
Ivshti (Ambire) patched:
GalloDaSballo (judge) commented:
