A Re-Entrancy Attack is a vulnerability in smart contracts where an external contract or malicious actor can repeatedly call back into the original contract before the first execution is complete, leading to unintended and often exploitative state changes. This allows the attacker to drain funds or manipulate contract logic by repeatedly withdrawing assets or executing functions. It arises when a contract sends funds to an external address and then makes an external call to that address before updating its own state. Preventing this requires careful sequencing of operations.
Context
The state of re-entrancy attacks remains a significant concern in smart contract security, despite being a well-known vulnerability, as new variations continue to emerge. Its situation involves ongoing efforts by developers to implement best practices, such as checks-effects-interactions patterns and re-entrancy guards, to mitigate this risk. A critical future development includes more sophisticated static analysis tools and formal verification methods to detect such vulnerabilities pre-deployment. News frequently reports on smart contract hacks where re-entrancy was the exploit vector.
A critical re-entrancy vulnerability in the GMX codebase allowed a threat actor to repeatedly execute withdrawal logic, resulting in a $42 million asset drain .
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