Glossary
Poly Network Hack (2021)
The August 2021 cross-chain exploit that stole ~611M USD across Ethereum, BNB Chain, and Polygon — almost all of it returned by the white-hat attacker within days.
On August 10, 2021, an attacker exploited a vulnerability in Poly Network's cross-chain contracts to authorize themselves as the keeper of the multisig that controlled bridge funds. They then minted and withdrew ~611 million USD of assets across Ethereum, BNB Chain, and Polygon — at the time the largest DeFi exploit ever.
In an unusual twist, the attacker began returning the funds within hours of the hack, eventually returning nearly all of it. Poly Network offered them a $500k bug bounty and a job, which they declined. The episode remains a unique case study in exploit-mitigation dynamics.