Some types of Curve factory pools, including one operated by AlchemixFi and one by JPEG'd, were exploited. The attack stemmed from an issue in the Vyper language, a smart contract programming language that is similar to Solidity. Early investigations suggested that versions of the Vyper compiler had improperly implemented a re-entrancy guard, leaving some projects vulnerable to that type of attack. Vyper tweeted an announcement that the versions were vulnerable, and urged "projects relying on these versions [to] immediately reach out to us".Curve itself lost $61 million to the exploit. AlchemixFi was exploited for around $13 million in assets, and JPEG'd suffered a $11 million loss. MetronomeDAO suffered a $1.6 million loss, Ellipsis Finance lost $68,600, and Debridge Finance lost around $24,600.
Altogether, somewhere between $88 million and $100 million was taken, though some exploits appeared to be whitehat actions intended to preserve funds. The primary exploiter also later returned some of the stolen funds, refunding the entire amount to AlchemixFi and 90% of funds to JPEG'd in exchange for a 10% "bug bounty".