By Why Is Harmony Rolling Back Its Blockchain?
Harmony plans to roll back its blockchain to a point before last week’s exploit after determining that attackers forged more than 3 trillion ONE tokens through a vulnerability that allowed previously valid transactions to be reused.
The Layer 1 blockchain said validators will roll back Shard 0 and Shard 1, the two chains that make up its sharded network, to immediately before the confirmed unauthorized mint. Blocks and transactions recorded after that point will be discarded as Harmony attempts to remove the forged tokens from the blockchain’s state.
The project considered several alternatives, including burning the unauthorized ONE, blacklisting wallets that received the tokens and migrating to a new version of the token. Harmony ultimately concluded that those approaches carried greater risks because the forged assets had already moved through exchanges, decentralized finance protocols and bridges.
“Of the options we studied, one fixed rollback window is the fairest and most secure,” Harmony said. “It applies one rule to everyone, removes the forged state, and carries the lowest risk of another attack or consensus failure.”
A rollback is a particularly disruptive response because legitimate transactions completed after the selected block will also disappear. Users and applications may therefore need to reconcile balances or repeat transactions once the network resumes from the earlier state.
How Were More Than 3 Trillion ONE Tokens Created?
Harmony initially confirmed the exploit on Aug. 12 after discovering unauthorized ONE minting. An independent researcher first identified 4 billion tokens created through empty blocks, but the project later found that the activity was substantially larger.
A subsequent reconstruction identified 3.01 trillion forged ONE tokens created across six transactions and sent to four exploiter wallets. One wallet successfully transferred nearly 2.4 trillion ONE in less than two minutes, an amount that would have been worth almost $3 billion at prices before the attack.
The vulnerability involved Harmony’s cross-shard receipt verification system. Valid receipts could reportedly be processed more than once, allowing an attacker to reuse the same transaction records to generate additional ONE tokens without a corresponding debit elsewhere on the network.
That effectively allowed new supply to be created without the economic activity that should normally support it. Harmony patched the vulnerability on Aug. 12 after detecting the attack, preventing the same method from being used again.
Investor Takeaway
The rollback removes the forged supply at the blockchain level, but it also reverses legitimate activity recorded after the selected block. For ONE holders, the immediate issue is therefore not only the exploit itself but how smoothly Harmony can restore balances, applications and cross-chain activity after rewriting part of the network’s transaction history.
Why Can’t Harmony Simply Burn The Forged ONE?
Harmony said it has traced nearly all of the unauthorized tokens to wallets or services, but tracing them does not mean they can all be safely destroyed.
Large quantities passed through decentralized exchanges, liquidity pools and bridges after the exploit. Once forged tokens are exchanged for legitimate assets or mixed with liquidity supplied by other users, burning balances linked to the attack can transfer losses to people who were not involved.
Blacklisting presents a similar problem. A wallet that received ONE from an exploiter may later have sent the tokens to another trader, protocol or centralized service. Freezing every address in that transaction chain could affect legitimate users and create uncertainty over which balances remain usable.
A token migration could isolate the compromised supply but would require exchanges, wallets, protocols and users to move to a new asset. Harmony instead chose to return the entire network to a known state before the exploit, accepting the cost of reversing later transactions in exchange for removing the forged supply in one step.
What Does The Rollback Mean For Harmony?
The decision places the focus on whether Harmony can coordinate validators, exchanges, bridge operators and decentralized applications around the rollback without creating additional balance discrepancies.
For users, the most important issue will be determining which transactions occurred after the rollback point and whether deposits, withdrawals, swaps or bridge transfers need to be repeated. Services that credited ONE based on transactions later removed from the chain may also need to reconcile their internal records.
The episode also exposes the risks created by cross-shard infrastructure. Harmony’s architecture divides activity across multiple shards to increase capacity, but communication between those shards depends on verification mechanisms that must ensure the same transaction cannot be processed twice.
The vulnerability has now been patched, but restoring the blockchain does not automatically restore confidence. Harmony will need to show that the underlying receipt-verification failure has been fully addressed and that similar replay attacks cannot create additional supply.
The rollback may eliminate the forged ONE from the official chain state, but the longer-term test will be whether users, validators and liquidity providers accept the reversal and continue using the network after one of the largest unauthorized token-minting incidents in its history.