Hackerdao Hack

On May 24th, Hackerdao token contract was attacked for 200BNB. The WBNB-Hackerdao pair has been drained in this transaction 0x04673c950....

Attacker transaction: https://bscscan.com/tx/0x04673c95…08422d

Blocksec transaction: https://versatile.blocksecteam.com/tx/bsc/0x04673c95…08422d

Attacker address: https://bscscan.com/address/0xcFc591dB…Cd1f82

Attacker contract: https://bscscan.com/address/0x24cb6980…9a4694

Victim contract: https://bscscan.com/address/0x94e06c77…13eC1C

Attack step by step:

1. The attacker used the logic of the Hackerdao contract vulnerability, in which the _transfer function incorrectly processes the uniswapV2 pair.
2. Then, if the recipient's address is the specified Uniswap pair (BSCUSD-Hackerdao pair, 0xbdb426a2…ae0225), the additional commission amount will be further reduced from the sender. This leads to a typical pattern of token attacks: if the balance of a Uniswap pair can be reduced without any swap (i.e. the difference between the recorded reserves and the actual token balances), there is a possibility of price manipulation.
3. The attack is carried out by switching from a pair of WBNB-Hackerdao to a pair of BSCUSD-Hackerdao, which leads to an unbalanced price.