Anchor Protocol Honeypot

Reported loss Not disclosed
BNB Chain
Honeypot

What happened

This record covers a BNB Chain token named "Anchor Protocol" (ANCHOR), deployed on 6 May 2021 at 0x5669f8af…0a473b. It shares a name with Terra's Anchor Protocol, whose governance token is ANC, but it is a separate token with no code link to that project. Its _transfer function has an owner switch, _feeEnabled: when it is on, any transfer into the PancakeSwap pair from an address other than the router, the owner or the contract debits the sender's full amount but credits the pair with only the remainder of amount divided by 100 base units, and burns the rest.

A holder's sale therefore either reverts in the pair's swap check or hands over the tokens for almost nothing, while buys and the owner's own transfers are unaffected. De.Fi's REKT database lists this ANCHOR token as an exit scam/honeypot, stating that the contract owner could disable transfers and so stop holders from selling.

How it happened

  1. The constructor stores the deployer as the private _owner, credits it the full 100,000,000 ANCHOR supply and creates the PancakeSwap pair.
  2. _feeEnabled starts as false, so trading, including sales, works normally at first.
  3. Only _owner can call setFeeEnabled(true). There is no function to transfer or renounce _owner.
  4. With the flag on, a sale reaches _transfer(holder, pair, amount). The holder's balance is reduced by the full amount, but fee = mul(div(amount, 100), 100) is amount rounded down to a multiple of 100 base units, so the pair receives at most 99 base units (under 0.0000001 ANCHOR at 9 decimals) and the fee is removed from _totalSupply.
  5. Because the pair receives almost nothing, a standard router sale fails the pair's reserve check and reverts, and a fee-on-transfer sale returns close to zero BNB. Transfers from the owner, the router or the contract, and transfers to any address other than the pair, are not taxed, so buys still work.

Protocol details

Classification Exchange (DEX)
Protocol Type Exit Scam/Honeypot
Affected asset / contract ANCHOR

Evidence

Same attack technique

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