On September 6, 2026, Liquid Network, the Bitcoin sidechain developed by Blockstream for faster, confidential transactions and asset issuance, disclosed that roughly 4,000 bitcoin valued at about $320 million had been withdrawn from its federation wallet.
The network described the parties involved as “purported white-hat hackers.” The incident drained approximately 95% of the bitcoin that backed L-BTC (the sidechain’s pegged bitcoin token), leaving the federation wallet with only around 197 BTC out of a prior balance near 4,200 BTC.
Liquid network immediately halted new transactions by disabling bridge nodes and asked exchanges to suspend L-BTC deposits and withdrawals. Other assets issued on Liquid, including USDT, DePix, and various tokenized real-world assets, were unaffected.
What Happened
The funds left through a standard peg-out process handled by SideSwap, a settlement platform authorized to process withdrawals from Liquid. SideSwap reported that a customer submitted 4,000 L-BTC at approximately 14:05 UTC. The tokens were burned on Liquid under a valid peg-out authorization, and the Liquid Federation released roughly 3,996 BTC to a Bitcoin address controlled by the actors about 23 minutes later.
Critically, Liquid stated that SideSwap’s Peg-out Authorization Key (PAK) was not compromised, nor were any other federation keys. The withdrawal used the normal 11-of-15 multisignature process of the federation rather than any emergency override path.
The receiving address later consolidated the funds and embedded an OP_RETURN message: “we are whitehats. contact us on chain.” Blockstream responded on-chain, directing contact to security@blockstream.com. The parties continued communicating via Bitcoin transactions and encrypted messages.
The Root Cause: An Elements Software Bug
The root cause of this Mega Hack comes as L-BTC used for the peg-out was not backed by real bitcoin. SideSwap and Liquid attributed the creation of these unbacked tokens to a bug in Elements, the open-source software a Bitcoin Core fork maintained primarily by Blockstream that powers Liquid. Nodes running Elements could not distinguish the invalid L-BTC from legitimate coins.
Independent technical analysis has focused on a range-proof caching issue in Elements’ confidential transactions implementation. Liquid hides transaction amounts for privacy, so every output must include a range proof confirming the value is non-negative and within bounds. Because verification is computationally expensive, nodes cache successful results.
Researchers identified problems in how the cache key was constructed. Earlier versions omitted key context (asset and script), allowing a previously verified proof to be reused inappropriately. A more recent change intended to fix the issue introduced its own problem: an unframed concatenation of variable-length fields that permitted preimage aliasing, so distinct (proof, commitment, asset, script) tuples could produce identical cache keys. An attacker could prime the cache with a valid proof and then submit an invalid transaction that hit the same cache entry, causing nodes to skip the real cryptographic check and accept the creation of unbacked L-BTC.
A related fix had been committed to the Elements repository in the days before the incident but had not yet appeared in a tagged release that production nodes were running.
This was not a classic private-key theft or multisig compromise. It was a consensus-level validation failure that allowed inflation of L-BTC, which was then redeemed for real BTC via the legitimate peg-out machinery.
Aftermath of the Cyberattack and Partial Recovery
The network remained paused while Blockstream and federation members worked on patches and investigated the chain split. Yesterday September 7, Blockstream posted a PGP-signed on-chain message confirming that bridge nodes had been patched and it was “safe to return the funds.”
The actors then returned 3,400 BTC approximately $269–270 million at prevailing prices to the federation wallet. They retained roughly 598.5 BTC (about $47 million), describing the retained amount in terms consistent with a bounty for identifying the vulnerability. Some observers, including Ledger CTO Charles Guillemet, questioned whether the episode truly qualified as pure white-hat activity, noting the scale of the drain and the decision to keep a substantial portion.
As of September 7–8, 2026 Liquid network has not fully resumed operations. Blockstream and federation members continued additional fixes, security improvements, and work to resolve the chain split before a safe restart. L-BTC remained under-collateralized relative to its original 1:1 design, though the partial return significantly narrowed the gap.
Liquid, launched in 2018, is a federated Bitcoin sidechain designed for rapid settlement, confidential transactions, and issuance of assets (stablecoins, tokenized securities, etc.).
The federation of member institutions collectively controls the bitcoin reserves that back L-BTC.
The incident highlights the risks inherent in complex sidechain software, especially confidential-transaction cryptography and caching optimizations, even when the underlying Bitcoin multisig and keys remain intact.
It also underscores the unusual nature of “white-hat” operations conducted at this scale: draining nearly an entire reserve, negotiating publicly on-chain, conditioning return on a patch, and retaining a large bounty. The episode ranks among the largest cryptocurrency security incidents of 2026 by value moved.
For users and exchanges, the immediate impact was a freeze on L-BTC movements.
Holders of other Liquid-issued assets face no direct loss of those tokens, though the pause disrupted related activity.
The long-term effects on trust in federated Bitcoin sidechains, the speed of Elements release cycles, and audit practices around validation caching remain to be seen.
Blockstream and the Liquid Federation have prioritized restoring full 1:1 backing, completing remaining security work, and carefully restarting the network. The self-described white-hat actors continue to hold the remaining bitcoin while discussions continue.
