The contract gates a function on 'caller is an EOA' via extcodesize(caller) == 0 or address.code.length == 0. This is bypassable: during a contract's own constructor its code size is still zero, so an attacker calls the gated function from a constructor.
// require(addr.code.length == 0); // 'must be EOA' // attacker: contract A { constructor(){ Victim.protectedMint(); } } // during A's constructor, A.code.length == 0 -> check passes.
// there is no reliable on-chain EOA check; use tx.origin == msg.sender // only with full awareness, or redesign to not require it require(msg.sender == tx.origin, "no contracts"); // still imperfect
Largest recorded losses in the same failure class — related, not the same bug:
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