SECURITY ALERT
The receipts were forged.
The signatures were not.
Ankr’s Ethereum cross-chain bridge lost roughly $286,000 to $305,000 on Monday morning after an attacker submitted five withdrawal receipts that all pointed to one real deposit on Optimism, according to security firms Blockaid, SlowMist and PeckShield.
The firms’ totals differ because they priced the tokens at different moments. Blockaid said about $292,000, PeckShield about $286,000, SlowMist about $304,500.
We have not found a statement from Ankr about the incident on its X account.
Who, or what, signed those five receipts?
What the firms say happened
A bridge lets a token on one chain be claimed on another. Ankr’s checks a signed receipt that says a deposit happened on Optimism, then releases tokens on Ethereum.
SlowMist says the attacker reused one genuine Optimism transaction five times and changed the recipient, the token and the amount in each receipt.
All five carried valid signatures from the bridge’s trusted signer, SlowMist says, and the withdrawal function released assets without checking the receipts against the real Optimism events.
SlowMist adds that where the unauthorised signatures came from is still under investigation, and that a signer compromise has not been confirmed.
Blockaid says that hours earlier the same attacker swept several Ankr operator wallets on Ethereum, Arbitrum and Linea into one new wallet, then funded the relayer from it. It puts those native sweeps at about 02:08 to 04:06 UTC.
Blockaid does not say the sweeps and the forged signatures are connected. Neither do we.
The Defiant reported that the bridge contract was still unpaused after the withdrawals.
Is a valid signature on a false receipt a stolen key, or a missing check?
The five transactions
We read the five transactions from public Ethereum RPC data. Each was sent by the same address to the bridge contract and succeeded. Each moved one token to one recipient.
| Time (UTC) | Block | Token | Amount |
|---|---|---|---|
| 08:09:35 | 26,376,043 | ankrETH | 82.91 |
| 08:09:47 | 26,376,044 | ANKR | 7,982,766 |
| 08:09:59 | 26,376,045 | ankrPOL | 515,206 |
| 08:11:23 | 26,376,052 | aPOLb | 5,372 |
| 08:11:59 | 26,376,055 | aETHb | 0.82 |
PeckShield counts the same tokens, with about 83 ankrETH worth roughly $192,000 as the largest piece. It says most of the proceeds were swapped into 103 ETH, about $217,000.
At about 10:48 UTC the recipient address held 104.72 ETH, by our read of the same data. That is not a freeze. It is a balance.
The bridge contract answered true to a paused() call at the same time. We do not know when it was paused or by whom.
What happens to holders of the wrapped tokens the bridge issues?
Evidence ledger
Attacker (tx sender): 0x9A88Dd45AE846A979705c9cFdfD0f229e592D703 (per SlowMist and Blockaid)
Recipient: 0x119D250b82C1cf5345dF5912EFb4B1a4107a1Aa6 (per SlowMist and Blockaid)
Bridge contract: 0xc437DF90B37C1dB6657339E31BfE54627f0e7181 (per SlowMist; labelled “Ankr: Bridge” on Etherscan)
Ethereum, ankrETH (82.91): 0x7310af5d53e08259915bc3547daf343d188b9c36db8dd6b3ff3b5e70565e88df
Ethereum, ANKR (7.98M): 0x90c563360cc343a640721662abe762e9ab9665aee0c22820b1656ff23bcfc891
Ethereum, ankrPOL (515K): 0xde2d5b455c0071698fec9c23a9c50f9ecdfd8efa96b4fbb48ed0620bd4c29b5c
Ethereum, aPOLb (5,372): 0x91ba1a9c81a1bb67ce7a2779d5b2de54b7aece166f67d9e3a31e29e4e13c2886
Ethereum, aETHb (0.82): 0x46e20d4c8cd43dece94f7a2a890a348fefcb0dc8310279658c8f836e758bdad0
SlowMist lists the five hashes above as the attack transactions and one Optimism transaction as the reused source. We checked the five on Ethereum ourselves.
Nothing has been reported frozen or returned. No attacker has been named, and we do not name one.
What is not known yet
The origin of the signatures. The final loss. Whether Ankr will reimburse anyone, and whether other Ankr bridge routes were touched.
Ankr has not said, in anything we could find, which tokens or users are exposed beyond the five transfers above.
Protect yourself
- If you use Ankr’s bridge, wait for a statement on Ankr’s official channels before sending or claiming anything.
- Treat any “recovery” or “compensation” link as hostile until Ankr publishes it itself. Fresh exploits draw phishers.
- If you have approved Ankr bridge contracts in the past, review them on a tool such as Revoke.cash and remove what you no longer use.
- Keep amounts in wrapped or bridged tokens in proportion to how much you trust the bridge behind them.
This is the latest incident on our board this week, after ACryptoS lost about $665,000 and Web3Auth’s recovery wallets.
How many bridges still trust a signature more than a ledger?
Corrections and new evidence: [email protected]
This article is for information only and is not investment advice.