Nerve Finance Hack

The attacker:

https://bscscan.com/address/0xd5476194…d69228

The transaction behind the attack:

https://bscscan.com/tx/0xea95925e…6fcf1d

The attacker:

- borrowed 50,000 BUSD using a flash loan from Fortube

- swapped 50,000 BUSD for 50,351 fUSDT from Ellipsis

- invoked the swap function of MetaSwap to swap 50,351 fUSDT for 36,959 Nerve 3-LP with a relatively big slippage

- invoked the removeLiquidityOneCoin() function of Nerve.3pool with the LP tokens (received in the previous step) to remove the liquidity of BUSD, i.e., 37,071 BUSD

- invoked the swapUnderlying() function of MetaSwap to swap BUSD for fUSDT, and received 51,494 fUSDT.

The attacker repeatedly executed the above steps to drain the liquidity of the MetaPool and finally harvested 900 BNB.

Stolen funds were deposited into Tornado Cash mixer:

https://bscscan.com/tx/0xcf43eefb…0aec90

https://bscscan.com/tx/0x55bd06a0…190a53

https://bscscan.com/tx/0x2dbc18c6…23067b

https://bscscan.com/tx/0x17cd04cb…334e7c

https://bscscan.com/tx/0xe5a0a058…4fa1f4

https://bscscan.com/tx/0x16ec28d4…896581

https://bscscan.com/tx/0x7f6b4313…0bb3c1

The rest were bridged though AnySwap:

https://bscscan.com/tx/0x0348cc92…2332a6

The swap function ignores the impact of the virtual price, which means the value of the LP token will be underestimated and more LP tokens could be swapped out. As a result, it is possible to harvest more pool stablecoins by first fetching back the liquidity of the underlying stablecoins with the corresponding LP token, and then swapping pool stablecoins by invoking the swapUnderlying() function.