Safe Gravity Honeypot

Reported loss Not disclosed
BNB Chain
Honeypot

What happened

Safe Gravity (SAFEGRAVITY) is a BNB Chain token deployed on 8 April 2021 at 0x563a9303…ca5873. Its internal _approve function stores the requested allowance only when the token owner is the hard-coded deployer address 0xBbE84f65…eed195; for every other holder it writes an allowance of zero. A PancakeSwap sale needs the router to move the holder's tokens with transferFrom, which subtracts the amount from that zero allowance and reverts, so ordinary holders cannot sell through the router while buys from the pair still work.

The owner can also mint any amount of new tokens to itself. The analyst cryptot3ddybear listed this contract among tokens using the same rigged-approval pattern, and De.Fi's REKT database lists SAFEGRAVITY as an exit scam/honeypot, stating that holders were restricted from selling.

How it happened

  1. The constructor mints the full supply of just under 100,000,000 SAFEGRAVITY (99999999999999999 with 9 decimals) to the deployer, who also becomes the Ownable owner.
  2. When any holder calls approve or increaseAllowance, _approve checks owner == address(0xBbE84f65D89A1d083470f771869F4e67f0eed195); for everyone else it sets the allowance to 0 and emits Approval(owner, spender, 0). A comment above the check reads "Gravity can be too strong and keep you on earth".
  3. A router sale calls transferFrom(holder, pair, amount). The function moves the tokens, then computes _allowances[sender][_msgSender()].sub(amount, ...) on a zero allowance, which reverts the whole transaction.
  4. Buys use the pair's plain transfer to the buyer, which has no allowance step, so purchases go through and the hard-coded deployer address can still approve the router and sell.
  5. mint(uint256 amount) is onlyOwner and adds any amount to the caller's balance and to total supply.

Protocol details

Classification Token
Protocol Type Exit Scam/Honeypot
Affected asset / contract SAFEGRAVITY

Evidence

Same attack technique

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