Bond Olympus DAO

Step-by-step

1. Craft and deploy a contract so that it passes the requirements.
2. Call redeem with the malicious contract as the token_

Detailed Description

The attack relies on an arbitrarily supplied token_ parameter. The attacker simply needs to construct a malicious contract as the token_. Most importantly, it should return a token that has been permitted by the victim contract to move funds when its _underlying() method is called.

    function redeem(ERC20BondToken token_, uint256 amount_)
    external
    override
    nonReentrant {
        if (uint48(block.timestamp) < token_.expiry())
            revert Teller_TokenNotMatured(token_.expiry());
        token_.burn(msg.sender, amount_);
        token_.underlying().transfer(msg.sender, amount_);
    }

The attacker chose to set _underlying() to the OHM address.

Luckily for the DAO, the attacker was a whitehack that later returned the funds.

Possible mitigations

• Implement a whitelist of allowed tokens.