What happened
On July 20, 2023, attackers drained the liquidity pools of FFIST and several similar tokens on BNB Smart Chain, for losses of about $110K. FFIST's transfer logic included an _airdrop() routine that sent tokens to pseudo-randomly generated addresses. The address was derived from inputs a caller can predict and control: the last airdrop address, the block number and the transfer's from/to addresses. The attacker could therefore pick a transfer that made the airdrop target the FFIST/USDT pair itself, reset the pair's FFIST balance to 1, and then buy the pool's USDT with a tiny amount of FFIST.
BlockSec Phalcon put the ~$110K figure as the total across a series of similar tokens. SolidityScan attributes about $110K to FFIST.
How it happened
- The attacker (
0xcc8617331849962c27f91859578dc91922f6f050) bought a small amount of FFIST with WBNB through PancakeSwap. - It computed a recipient address that, combined with
lastAirdropAddress(), the current block number and the sender, would make_airdrop()produce the FFIST/USDT pair's address. - It sent a 0 FFIST transfer to that recipient. The transfer hook's airdrop then hit the pair and, per Phalcon, set the pair's FFIST balance to 1.
- It called
sync()on the pair so the reserve matched the collapsed FFIST balance, which made FFIST extremely expensive in USDT terms. - It sold its FFIST back through the pair for the pool's USDT and converted to WBNB (tx
0x199c4b88...9f0e0).
Protocol details
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