On June 16th, 2022, Inverse Finance was attacked, leading to the loss of more than 1M. The attack transaction is https://versatile.blocksecteam.com/tx/eth/0x958236266991bc3fe3b77feaacea120f172c0708ad01c7a715b255f218f9313c. The root cause is that the price oracle utilized by Inverse Finance has been manipulated.
The attacker burrowed 27,000 WBTCs from Aave with flashloan first. After that, 225 of them were deposited into Curve and 5,375 crv3crypto was minted. The attacker deposited the 5,375 crv3crypto into the yvCurve-3Crypto and got 4,906 Yearn cToken, which will be used as the collateral in Inverse Finance.
The remaining 26,775 WBTC is used to manipulate the price of the collateral. The attacker swapped 26,775 WBTC and got 75,403,376 USDT back. The swap lift the price of the oracle from 979 to 2,831.
As we can see from the function
borrowAllowed, it will check whether the user can borrow the specified amount of tokens with the deposited collaterals.
getHypotheticalAccountLiquidityInternal will be used to check whether the borrow behavior is safe. The price of the collateral is obtained with
getUnderlyingPrice invokes function
latestAnswer to get the result. As mentioned before, the 26,775 WBTC is used to swap the USDT, resulting in the lifting of collateral price.
In this case, the attacker can borrow a large amount of (i.e., 10,133,949) DOLA, whose value is more than the deposited collateral.
Finally, the attacker swapped the 75,403,376 USDT back to 2,662,649 WBTC, and swapped the burrowed 10,133,949 DOLA to 9,881,355 3Crv, which is further removed from the liquidity pool to get 10,099,976 USDT.
Then, 10,000,000 of the 10,099,976 USDT was swapped to WBTC again and used to repay the flashloan. Now the attack is completed. The attacker earns 99,976 USDT and 53.2 WBTC from this attack.
This is a traditional price manipulation attack. We are surprised that why such an attack can happen nowadays, this incident serves as a wake-up call for DeFi protocols to reinforce their security systems.
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