Bond_OlympusDAO

title	Bond Olympus DAO
description	Exploiting arbitrary token parameters in redemption functions
type	Exploit
network	ethereum
date	2022-10-21
loss_usd	300000
returned_usd	300000
tags	data validation
subcategory
vulnerable_contracts	0x007FE7c498A2Cf30971ad8f2cbC36bd14Ac51156
tokens_lost	OHM
attacker_addresses	0x443cf223e209E5A2c08114A2501D8F0f9Ec7d9Be 0xa29e4fe451ccfa5e7def35188919ad7077a4de8f
malicious_token
attack_block	15794364
reproduction_command	forge test --match-contract Exploit_OlympusDao -vvv
attack_txs	0x3ed75df83d907412af874b7998d911fdf990704da87c2b1a8cf95ca5d21504cf
sources	title url Peckshield Twitter Thread https://twitter.com/peckshield/status/1583416829237526528 title url 0xbanky.eth Writeup https://mirror.xyz/0xbanky.eth/c7G9ZfTB8pzQ5cCMw5UhdFehmR6l0fVqd_B-ZuXz2_o

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.

Related

• AnySwap Permit Attack - Arbitrary token parameter to drain user funds
• Compound TUSD Integration - Token address validation bypass
• LyraDepositWrapper - Unvalidated address grants arbitrary token approvals