Liquid's "white hats" gave back 3,400 BTC. Blockstream is negotiating for the other 600

Nobody stole a key. Which is the strangest part of the largest bitcoin loss of the year, and the part that should worry you if you settle real money on a federated sidechain.

On Saturday 6 September 2026 someone exploited a bug in the way Liquid nodes cache range-proof verifications, and created roughly 4,000 L-BTC that no bitcoin in reserve stood behind. Those tokens went to SideSwap, a federation member holding a peg-out authorisation key, which processed them like any other withdrawal. Twenty-three minutes later, by SideSwap's account, the federation had paid nearly four thousand real bitcoin to a customer address.

Liquid's reserve fell from about 4,205 BTC to 197.

The multisig was not broken. It was told a lie.

Liquid's incident report is careful, and correct, about the second half of that. "No keys were compromised. The Liquid Federation functionaries were not hacked ... The peg-out mechanism that authorizes withdrawals to whitelisted addresses operated as designed."

Eleven of the fifteen functionaries signed, which is exactly what the scheme was built to require. They were handed tokens that every node on the network considered valid, "because the validation failure occurred at the transaction level before the peg-out was initiated."

So this was not a theft in the ordinary sense. Compare it with the case we wrote up in The biggest crypto theft in US history went through a Google Drive, or with January's Step Finance loss, where attackers got at executives' devices and the keys those devices held. Here the chain simply believed something false about its own supply (and USDT and the other Liquid-issued assets were untouched).

The phrase "white hat" did not survive the weekend

Whoever did this described themselves that way in an on-chain message. "Please fix the bug first. The chain is under risk at latest commit right now. Make sure every node is patched. Then we will transfer the money back safely after confirming the fix."

By Monday 3,400 BTC had come back. About 598.5 BTC, worth roughly $47 million, had not. "Discussions between Blockstream and the individuals responsible are ongoing to secure the return of the remaining funds," Liquid said on Tuesday. On Wednesday Blockstream shipped Elements v23.3.4, reviewed by the Bitcoin Red Team, Alpen Labs and others, hardening the cache keys used for range proofs. It also told users to treat any "unsolicited 'white-hat' or bounty outreach" as a scam.

Ledger's chief technology officer, Charles Guillemet, stopped extending the benefit of the doubt once the 600 stayed out. "If this was ever a negotiated reward under an encrypted contract signed on-chain, it looks more like extortion than white-hat hacking!"

What do you call keeping 15 percent of $320 million? A bounty, set by the person taking it.

We would expect Blockstream to pay it, in the sense of accepting what came back as the recovery and quietly calling the rest a reward, because the alternative is restoring a network with a nine-figure hole in it while the federation's members are exchanges and brokers with customers of their own. That is probably the market price of a bug that lets somebody print bitcoin.

The structural problem outlasts the negotiation

Liquid's security model is that a federation of more than 80 firms cannot be corrupted member by member. Saturday showed the model has nothing whatever to say about a consensus bug, because every honest node validated the fake.

A federated peg seems to be only as sound as the least-reviewed line in its verification code. And Elements has far fewer eyes on it than Bitcoin Core does.

That is awkward for the pitch that Liquid is where bitcoin treasury companies and tokenised securities should settle. Five such products listed on Bitfinex Securities through Liquid in the first week of September, and their issuers have spent the days since explaining a paused chain to holders.

The sidechain is still down. Blockstream's plan is to resume block production with pegs suspended, replay valid transactions, and reopen pegs "once the network state has been fully restored including a return of funds." We would expect pegs to reopen before 30 September with the remaining coins still gone and the reserve made whole by Blockstream or by federation members.

If all of it comes back before the pegs reopen, the white hats were what they said they were, and we will owe them the label.