Submitted by 0xdeadbeef0x
Vault creator can prevent users from claiming rewards from the staking contract. This can boost his liquidity and lure depositors to stake vault tokens. He can present a high APY and low fee percentage which will incentivize stakers.
When the staking contract is empty of stakes, he can change the settings and claim all the rewards to himself.
Vault creator receives management fees from two places:
Users can claim staking rewards by calling the claimRewards function of the staking contract: 
https://github.com/code-423n4/2023-01-popcorn/blob/d95fc31449c260901811196d617366d6352258cd/src/utils/MultiRewardStaking.sol#L179
As can be seen above, if there is an escrow specified, percentage of rewards are sent to the escrow account through _lockToken: 
https://github.com/code-423n4/2023-01-popcorn/blob/d95fc31449c260901811196d617366d6352258cd/src/utils/MultiRewardStaking.sol#L201
escrow.lock will send fee to feeRecipient that is passed in the constructor of the escrow contract when there is a fee percentage defined. (This can be low in order to incentivize stakers) 
https://github.com/code-423n4/2023-01-popcorn/blob/d95fc31449c260901811196d617366d6352258cd/src/utils/MultiRewardEscrow.sol#L111
The issue rises when feeRecipient is set to the zero address (0x0). safeTransfer will revert and the transaction of claiming rewards will fail (all the way through the claimRewards on the staking contract`.
User funds will be locked in the contract.
The vault creator can decide when is the right time to open the rewards up (maybe when nobody is invested in the vault) by changing the fee percentage to 0 using setFees, which bypass sending fees to feeRecipient. if the vault owner will be the only saker, he can receive all the deposited tokens back.
Foundry POC
Add the following test:
test test__no_rewards
VS Code, Foundry
Validate in the initialization of the staking contracts that escrow.feeRecipient is not the zero address.
RedVeil (Popcorn) confirmed, but disagreed with severity 
LSDan (judge) decreased severity to Medium 
