Symbiogenesis Rug Pull

Reported loss $54K
Rugpull

What happened

SYSIS (Symbiogenesis) is an ERC-20 token on Ethereum that traded on Uniswap. PeckShield's alert on 2023-11-28 says address 0x8B54...8cca swapped 99,999,999,999,999 SYSIS for 26.67 WETH (about 53.7K USD) and that the token fell 100 percent. De.Fi's REKT database lists it as a rug pull exit scam with 53,639 USD of liquidity (26.67 ETH) removed from the Uniswap pool, with the funds then moved to another EOA address through a smart contract.

The verified source looks like a standard OpenZeppelin token but is not. Its _transfer does not check the sender's real balance: it asks an external contract for the number, and that contract's address is derived from the constructor argument. The token has a fixed 50,000,000 supply, yet the swap PeckShield reports is far larger than that supply, which is the kind of amount this check would let an attacker-chosen contract approve. No source opened here shows what that external contract returned.

Deployer address: 0xf5e228B8…EfC483. Scammer address listed by De.Fi: 0x95a6FcB5…79C180. Liquidity removal transaction listed by De.Fi: 0x62d292c0…0ec58c. Malicious contract listed by De.Fi: 0x8B544F47…eF8cca.

How it happened

  1. The deploy-time _mint(msg.sender, totalSupply) call uses its amount argument for something other than the supply: uint160 z = uint160(amount) + u; address p = address(z); x = XOL(p); with u = 834774399394859312355. The deployer's constructor argument therefore chooses the address stored in x, and the code then overwrites amount = 50000000 * 10 ** 18; so the minted supply is fixed at 50M whatever was passed.
  2. Every transfer begins by reading the sender's balance from that external contract instead of from storage: uint256 senderBalance = balanceoF(sender);, where balanceoF returns x.squirrel(true, bytes32(0), sender). Only after that does it run require(senderBalance >= amount, ...).
  3. The stored balance is then set from the external number, not debited from the real one: _balances[sender] = senderBalance - amount; inside an unchecked block, while the recipient is credited normally with _balances[recipient] += amount;. A contract that returns a large value for one sender lets that sender move more tokens than it holds and have the recipient, including the Uniswap pair, credited for them. A contract that returns 0 for a holder makes that holder's transfers and sells revert.
  4. balanceOf still reads _balances, so wallets and explorers show ordinary-looking balances. The token has no owner, mint function or pause switch; the control sits entirely in the external contract that x points to, whose code is not part of the verified source.
  5. What happened, per PeckShield: on 2023-11-28 address 0x8B54...8cca swapped 99,999,999,999,999 SYSIS for 26.67 WETH, far above the 50,000,000 token supply, and the price fell to zero. De.Fi's REKT database describes the same 26.67 ETH (53,639 USD) as liquidity removed from the Uniswap pool and moved to another EOA through a smart contract. Neither source says what the external contract at x returned.

Protocol details

Classification Token
Protocol Type Exit Scam/Rugpull
Affected asset / contract SYSIS

Evidence

Same attack technique

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