Bitcoin sidechain Liquid was exploited on Sunday, with approximately 4,000 BTC transferred out. Blockstream has refused to pay a ransom for the roughly 598.5 BTC still held by the attacker. The attacker returned 3,400 BTC on Monday. Liquid resumed block production on Thursday, but peg-out redemptions remain disabled. The vulnerability stemmed from node caching of range proof verification results, which the attacker exploited to mint L-BTC out of thin air and exchange it for reserve Bitcoin. Blockstream patched the issue within ten hours.