Ether Drain

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Use Case

Many protocols use ether as a collateral asset. If the protocol is exploited, the attacker can drain all the ether from the protocol. Having assertions in place that prevent draining can be helpful to prevent or at the very least slow down the rate at which a protocol is drained.

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Explanation

Check that the ether balance of a contract does not decrease by more than 50% in a single transaction.

Note: This does not prevent draining from happening, as a somewhat capable attacker would just drain 49% of the ether in a single transaction. It’s better than nothing and if mitigation is in place it could pause the protocol on a draining attempt.

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Code Example

pre: Get ether balance of contract before transaction

post: Ether balance of contract is not decreased by more than 50%