13. Reentrancy Attack

Problem

• If we call a function of another contract in the middle of a withdraw, the other contract may have malicious function which may recalls the withdraw function again and again resulting in draining of all the funds

• https://solidity-by-example.org/hacks/re-entrancy/

Solution (Easy Way)

• Always call another contract in the last step of transaction

• Updated balances (change state) before calling another contract

Solution (Mutex)

• Use a mutex

• Openzepplin provides a way to safeguard i.e a Modifier

  • Contract name is ReentrancyGuard

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