ERC20 Drain

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Use Case

One of the most common things that happen when a protocol is exploited is that the attacker drains all the tokens 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 token 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 tokens 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 erc20 token balance of contract before transaction

post: erc20 token balance of contract is not decreased by more than 50%