What happened
Instaswap (INSTA) is a BEP-20 token deployed on BNB Chain on 28 April 2021 at 0xa9325729…cf99b9. Its verified code lets the deployer turn on a so-called fee with setFeeEnabled(true). While it is on, any transfer into the PancakeSwap pair from anyone other than the owner, the router or the token contract debits the sender's full amount but credits the pool with only the remainder after rounding down to a multiple of 100 base units, burning the rest.
A sale therefore delivers almost no tokens to the pool, so it either reverts or burns the seller's tokens for near-zero BNB, while the owner stays exempt and can still sell. There is no function to transfer or renounce ownership. De.Fi's REKT database lists the token as an exit scam/honeypot.
How it happened
- The constructor gives the whole 100,000,000 INSTA supply to the deployer, stores it as
_owner, and creates the INSTA/WBNB pair on PancakeSwap._feeEnabledstarts asfalse, so buying and selling first work normally. - The owner, and only the owner, can call
setFeeEnabled(bool). The contract has notransferOwnershiporrenounceOwnership, so this switch stays with the deployer. - When
_feeEnabledistrueand a transfer goes touniswapV2Pairfrom an address other than the router, the owner or the contract,_transferfirst subtracts the fullamountfrom the sender, then computesfee = mul(div(amount, 100), 100): the amount rounded down to a multiple of 100 base units (0.0000001 INSTA). - The pool is credited only
amount - fee, at most 99 base units, andfeeis subtracted from_totalSupply. Almost all of a holder's sale is destroyed rather than delivered, so the swap either fails the pair's balance check or pays out close to nothing. - Buys (transfers from the pair) and wallet-to-wallet transfers are unaffected, and the
from != _ownerexemption lets the deployer keep selling into the pool that buyers funded.
Protocol details
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