Poster: FlashGuard: Real-time Disruption of Non-Price Flash Loan Attacks in DeFi

Abstract

Flash loan attacks threaten decentralized finance (DeFi) protocols, which constitute a Total Value Locked (TVL) of more than 106 billion. These attacks exploit the atomicity property in blockchains to drain funds within a single block. Existing research overlooks the mitigation of non-price flash loan attacks, which mostly exploit zero-day vulnerabilities. These attacks are challenging to detect as they are highly time-sensitive and each instance of the attack is complex and has a unique pattern. To address this challenge, we present FlashGuard, a runtime detection and mitigation framework for non-price flash loan attacks. FlashGuard communicates directly with the miners and bypasses the public mempool, where attack transactions usually reside. We utilize the temporary time window where transactions are visible in the mempool but not yet confirmed. Once the attack is detected, FlashGuard dispatches a dusting counter-transaction for the victim contract to the miners directly within the same block to disrupt the attack's atomicity and change the smart contract state. This forces the malicious transaction to revert. FlashGuard ensures that the series of operations that are required for a non-price flash loan attack cannot be completed atomically, leading to a failure of the attack. Our evaluation using 20 historical attacks that exploited protocol vulnerabilities shows an outstanding detection rate for FlashGuard with minimal false positives, and effective attack disruption and indicates that FlashGuard could have rescued about $405.71 million in losses.