While cryptocurrency hacks are not uncommon, instances where attackers take significant risks only to gain minimal rewards are rare. Such a scenario unfolded on Sunday when an attacker exploited a vulnerability in the Hyperbridge cross-chain gateway, connecting various blockchains, and minted 1 billion Polkadot tokens, valued at $1.19 billion, on the Ethereum network, only to sell them for around $237,000 worth of ether. This exploit highlights the ongoing issue of bridge vulnerabilities in 2026, following a $270 million drain on Solana's Drift Protocol last month and a social engineering attack that compromised infrastructure. The attack targeted the bridge contract, not Polkadot's core network, and the native DOT token remained unaffected.
The vulnerability was found in the validation process of incoming cross-chain messages by Hyperbridge's EthereumHost contract before passing them to the TokenGateway. Bridges, which facilitate the transfer 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, making them susceptible to attacks that can grant unlimited supply control. The attack began with the submission of a forged message via dispatchIncoming, which was 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 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 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 attacker received only a fraction of a cent per token due to the overwhelming amount of 1 billion tokens and the limited available liquidity. On a deeper pool or a higher-value bridged asset, the same vulnerability would have resulted in significantly larger losses. As of Monday morning, DOT was trading just under $1.20.
CertiK confirmed the exploit, stating that the attack vector was the Hyperbridge gateway contract and 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.