Mummy Token Rug Pull

What happened

Mummy Token (Mummy) was a reward token of Zombie Farm, a BNB Chain yield farm, minted by the farm contract CoffinChef at 0xb1f5b0E5…3f252e. The CoffinChef's owner can set any pool's deposit fee as high as 100% at any time, and the fee is sent to the fee address, so a new deposit can be taken entirely and credit the depositor nothing. The owner can also change the Mummy emission rate with no limit, and every emission mints an extra 10% to the developer address.

The owner is still 0xBA976F79…dddD7a, the address that deployed the token. De.Fi's REKT database lists Mummy as an exit scam; no transaction showing these settings being used was found.

How it happened

1. add and set are onlyOwner and accept a deposit fee up to 100%: require(_depositFeeBP <= 10000, "set: invalid deposit fee basis points"). set works on existing pools.
2. In deposit, the fee goes straight to feeAddress and the user is credited only the rest: user.amount = user.amount.add(_amount).sub(depositFee). At 10000 basis points a new deposit is credited zero. Tokens already staked stay withdrawable through withdraw and emergencyWithdraw.
3. updateEmissionRate(uint256 _mummyPerBlock) is onlyOwner with no bounds. Each updatePool mints the reward to the CoffinChef and an extra mummyReward.div(10) to devaddr, so the owner can inflate the Mummy supply and the developer share with it.
4. The Mummy token itself burns 5% of every transfer except transfers to the burn address, so each buy, sell or move of Mummy delivers only 95%.
5. renounceOwnership exists, but the owner is still the token's deployer, so these settings remain available.

Protocol details

Classification Token

Protocol Type Exit Scam/Rugpull

Affected asset / contract Mummy

Protocol links Website

Evidence

• report Report bscscan.com
• address Zombie Farm CoffinChef verified source code on BscScan bscscan.com
• analysis Sourcify exact match for 0xb1f5b0E504C46c1c0d115e4E1Ee4c6BdF63f252e on BNB Chain repo.sourcify.dev
• analysis Sourcify exact match for MummyToken 0x6238BCe7aae6a693e4463e5AC6b5b3227E104E0B on BNB Chain repo.sourcify.dev
• analysis Zombie Farm docs: MUMMY TOKEN zombiefarm.gitbook.io