withdraw_underlying_to_claim can be used by an attacker for sandwitch attacks.
Summary
The withdraw_underlying_to_claim function can be called by anyone and also has _min_weth_out which is controlled in the parameters, this function can be used to withdraw underlying tokens from alchemix with _min_weth_out low, so that an attacker can sandwitch this transaction and the vault would loose some tokens.
Vulnerability Detail
The function withdraw_underlying_to_claim is used to withdraw the underling tokens from alchemix to the vault. The function calls IAlchemist(self.alchemist).withdrawUnderlying internally with the receiver set to the vault address and the _min_weth_out is controlled by the attacker.
Assuming a scenario where the fund_receiver repays the loan and the tokens are available to be withdrawn and the amount is large enough. Then the attacker can call withdraw_underlying_to_claim with some less gas amount and sandwich it with a transaction. This would lead to the vault receiving less token (as the minimum value is set by attacker). It can be argued that alchemix would revert the transaction if the loss is greater than the maxLoss set in alchemix, but the attacker can still gain and the legitimate users would still loose some amount of ETH that is set on alchemix by setMaximumLoss function. This value can
def withdraw_underlying_to_claim(_amount_shares: uint256, _min_weth_out: uint256):
"""
@notice
Withdraws _amount_shares and _min_weth_out from Alchemix to be distributed
to token holders.
The WETH is held in this contract until it is `claim`ed.
@audit can be used for sandwitch attacks
"""
amount_withdrawn: uint256 = self._withdraw_underlying_from_alchemix(_amount_shares, self, _min_weth_out)
self._mark_as_claimable(amount_withdrawn)
log Claimable(amount_withdrawn)
Tool used
Manual Review
Recommendation
This function can be made callable only by users/owner.
psy4n0n
high
withdraw_underlying_to_claimcan be used by an attacker for sandwitch attacks.Summary
The
withdraw_underlying_to_claimfunction can be called by anyone and also has_min_weth_outwhich is controlled in the parameters, this function can be used to withdraw underlying tokens from alchemix with _min_weth_out low, so that an attacker can sandwitch this transaction and the vault would loose some tokens.Vulnerability Detail
The function
withdraw_underlying_to_claimis used to withdraw the underling tokens from alchemix to the vault. The function callsIAlchemist(self.alchemist).withdrawUnderlyinginternally with the receiver set to the vault address and the_min_weth_outis controlled by the attacker.Assuming a scenario where the fund_receiver repays the loan and the tokens are available to be withdrawn and the amount is large enough. Then the attacker can call
withdraw_underlying_to_claimwith some less gas amount and sandwich it with a transaction. This would lead to the vault receiving less token (as the minimum value is set by attacker). It can be argued that alchemix would revert the transaction if the loss is greater than the maxLoss set in alchemix, but the attacker can still gain and the legitimate users would still loose some amount of ETH that is set on alchemix bysetMaximumLossfunction. This value canImpact
Partial loss of user funds.
Code Snippet
https://github.com/sherlock-audit/2023-02-fair-funding/blob/main/fair-funding/contracts/Vault.vy#L394
Tool used
Manual Review
Recommendation
This function can be made callable only by users/owner.
Duplicate of #121