Submitted by hansfriese
https://github.com/code-423n4/2022-05-backd/tree/main/protocol/contracts/StakerVault.sol#L98-L102
https://github.com/code-423n4/2022-05-backd/tree/main/protocol/contracts/StakerVault.sol#L342-L346
https://github.com/code-423n4/2022-05-backd/tree/main/protocol/contracts/StakerVault.sol#L391-L395
StakerVault.unstake(), StakerVault.unstakeFor() would revert with a uint underflow error of StakerVault.strategiesTotalStaked, StakerVault._poolTotalStaked.
Currently it saves totalStaked for strategies and non-strategies separately.
uint underflow error could occur in these cases.
Scenario 1.
Even if it would succeed for this strategy but it will revert for other strategies because StakerVault.strategiesTotalStaked is less than correct staked amount for strategies.
Scenario 2.
There is a transfer between strategy and non-strategy using StakerVault.transfer(), StakerVault.transferFrom() functions.
In this case, StakerVault.strategiesTotalStaked and StakerVault._poolTotalStaked must be changed accordingly but there is no such logic.
Solidity Visual Developer of VSCode
You need to modify 3 functions. StakerVault.addStrategy(), StakerVault.transfer(), StakerVault.transferFrom().
danhper (Backd) confirmed 
Alex the Entreprenerd (judge) commented:
