While crypto hacks are common, cases where attackers take significant risks and end up with relatively minor gains are rare. Such a scenario occurred on Sunday when an attacker exploited a vulnerability in Hyperbridge's cross-chain gateway, which connects different blockchains. The attacker successfully minted 1 billion Polkadot tokens, valued at $1.19 billion, on Ethereum and sold them for around $237,000 worth of ether. This incident adds to the growing list of bridge vulnerabilities in 2026, including a $270 million Drift Protocol drain on Solana last month.
The exploit targeted the bridge contract and not Polkadot's core network, with the native token DOT 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 movement of coins between blockchains, 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 unfolded when the attacker submitted a forged message via dispatchIncoming, which was routed to TokenGateway.onAccept. The request receipts check, which should have verified the message against a valid cross-chain state commitment from Polkadot, stored an all-zeros commitment value, indicating that the proof validation was either absent or circumventable for this specific call path. The gateway processed the message as legitimate, and the accepted message 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 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 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 produced significantly larger losses. As of Monday morning, DOT trades just under $1.20. CertiK flagged 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 not publicly commented on the exploit or disclosed whether other bridged token contracts using the same gateway are vulnerable to the same forged-message attack vector.