While cryptocurrency hacks are not unusual, instances where attackers take significant risks only to gain minimal profits are rare. Such a scenario unfolded on Sunday. An attacker exploited a vulnerability in the Hyperbridge cross-chain gateway, which connects multiple blockchains, and minted 1 billion Polkadot tokens (valued at $1.19 billion) on Ethereum before selling them for roughly $237,000 in ether. This incident contributes to the growing list of bridge vulnerabilities in 2026, including a $270 million drain on Solana's Drift Protocol last month and a social engineering attack involving compromised infrastructure.
The exploit targeted the bridge contract and not Polkadot's core network, with the native DOT token remaining unaffected. The vulnerability was found in how Hyperbridge's EthereumHost contract validates incoming cross-chain messages before passing them to the TokenGateway.
Bridges, which facilitate the transfer of coins between different blockchains, are often the weakest link in cross-chain architecture due to their admin-level control over token contracts on destination chains. This means a single validation failure can grant an attacker the ability to mint an unlimited supply of tokens. The attack began with the attacker submitting a forged message via dispatchIncoming, which was then routed to TokenGateway.onAccept. The request receipts check failed to verify the message against a valid cross-chain state commitment from Polkadot, suggesting that the proof validation was either absent or could be circumvented for this specific call path.
As a result, the gateway processed the message as legitimate. The accepted message then executed changeAdmin 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 transferred them to a Uniswap V4 DOT-ETH pool via Odos Router V3, extracting approximately 108.2 ETH across multiple swaps at slightly different prices. However, the limited liquidity in the bridged DOT pool on Ethereum worked against the attacker, capping their profit. The pool's limited depth meant that the 1 billion tokens overwhelmed the available liquidity, resulting in the attacker receiving only a fraction of a cent per token.
On a deeper pool or a higher-value bridged asset, the same vulnerability would have led to significantly larger losses. 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.