Reentrancy Attack Vector

A reentrancy attack occurs when an external contract calls back into the original contract before the first invocation is finished. This allows the attacker to repeatedly withdraw funds or manipulate state variables before the contract updates its internal balance.

In the context of cryptocurrency, this is a classic exploit that targets the way smart contracts handle external calls. If the contract does not implement checks-effects-interactions patterns, it remains highly susceptible to this flaw.

It effectively bypasses security controls by tricking the contract into believing the previous transaction is still valid. Proper implementation of mutex locks or state updates before transfers is essential to mitigate this vulnerability.