Cryptocurrency hacks are a common occurrence, but instances where attackers take significant risks and end up with relatively small gains are rare. Such a scenario unfolded on Sunday when an attacker exploited a vulnerability in the Hyperbridge cross-chain gateway, which connects different blockchain networks.
The attacker successfully minted 1 billion Polkadot tokens, valued at $1.19 billion, on the Ethereum network and sold them for approximately $237,000 worth of ether. This exploit highlights the growing concern of bridge vulnerabilities in 2026, following a $270 million Drift Protocol drain on Solana last month. The targeted bridge contract, rather than Polkadot's core network, was the point of weakness. The native DOT token remained unaffected.
The vulnerability stemmed from the validation process of incoming cross-chain messages in Hyperbridge's EthereumHost contract. Bridges, which facilitate the transfer of coins between blockchain networks, are often the weakest link in cross-chain architecture due to their admin-level control over token contracts on destination chains.
A single validation failure can grant an attacker the ability to mint an unlimited supply of tokens. The attack began when the attacker submitted a forged message via dispatchIncoming, which was then routed to TokenGateway.onAccept.
However, the request receipts check failed to verify the message against a valid cross-chain state commitment from Polkadot, allowing the gateway to process the message as legitimate. The accepted message executed a changeAdmin function on the bridged Polkadot token contract, transferring admin rights to the attacker's address. With admin control, the attacker minted 1 billion tokens in a single transaction and sold them through Odos Router V3 into a Uniswap V4 DOT-ETH pool, extracting roughly 108.2 ETH across multiple swaps at slightly different prices. The limited liquidity of the bridged DOT pool on Ethereum worked against the attacker, capping their profit.
If the attack had occurred on a deeper pool or a higher-value bridged asset, the losses would have been significantly larger. As of Monday morning, DOT was trading just under $1.20. CertiK identified the exploit, confirming that the attack vector was the Hyperbridge gateway contract and that the attacker profited approximately $237,000 from minting and selling the bridged tokens. Hyperbridge has yet to publicly comment on the exploit or disclose whether other bridged token contracts using the same gateway are vulnerable to the same forged-message attack vector.