Approximately 4,000 BTC (~$320M) was withdrawn from the Liquid Federation reserve after an attacker exploited a rangeproof cache collision in the Elements software, minting unbacked L-BTC and redeeming it for real BTC.
The attacker self-identified as a "white hat" and returned ~85% of funds after the vulnerability was patched — but ~598.5 BTC (~$47M) remains unreturned.