Submitted by smilingheretic, also found by unforgiven_
https://github.com/code-423n4/2022-04-mimo/blob/b18670f44d595483df2c0f76d1c57a7bfbfbc083/core/contracts/liquidityMining/v2/PARMinerV2.sol#L159-L165
https://github.com/code-423n4/2022-04-mimo/blob/b18670f44d595483df2c0f76d1c57a7bfbfbc083/core/contracts/liquidityMining/v2/GenericMinerV2.sol#L88-L94
Users aware of this vulnerability could effectively steal a portion of liquidity mining rewards from honest users.
Affected contracts are: SupplyMinerV2, DemandMinerV2, PARMinerV2
VotingMinerV2 is less affected because locking veMIMO in votingEscrow  triggers a call to releaseMIMO of this miner contract (which in turn updates users boost multiplier).
Lets focus here on SupplyMinerV2. The exploits for other liquidity mining contracts are analogous.
Both Alice and Bob deposit 1 WETH to coreVaults  and borrow 100 PAR from coreVaults. They both have no locked veMIMO.
Now they wait for a month without interacting with the protocol. In the meantime, SupplyMinerV2 accumulated 100 MIMO for rewards.
Alice locks huge amount of veMIMO in votingEscrow, so now her boostMultiplier  is 4.
Lets assume that Alice and Bob are the only users of the protocol. Because they borrowed the same amounts of PAR, they should have the same stakes for past month, so a fair reward for each of them (for this past month) should be 50 MIMO. If they simply repay their debts now, 50 MIMO is indeed what they get.
However if Alice calls supplyMiner.updateBoost(alice) before repaying her debt, she can claim 80 MIMO and leave only 20 MIMO for Bob. She can basically apply the multiplier 4 to her past stake.
Both Alice and Bob deposit 1 WETH to coreVaults  and borrow 100 PAR from coreVaults. Bob locks huge amount of veMIMO in votingEscrow for 4 years, so now his boostMultiplier is 4.
Alice and Bob wait for 4 years without interacting with the protocol.
SupplyMinerV2 accumulated 1000 MIMO rewards.
Because of his locked veMIMO, Bob should be able to claim larger reward than Alice. Maybe not 4 times larger but definitely larger.
However, if Alice includes  a transaction with call supplyMiner.updateBoost(bob) before Bobs vaultsCore.repay() , then she can claim 500 MIMO. She can effectively set Bobs boostMultiplier for past 4 years to 1.
Tested in Foundry
I have 2 ideas:
m19 (Mimo DeFi) confirmed and commented:
