While cryptocurrency hacks are common, instances where attackers take significant risks only to walk away with relatively modest gains are rare. Such a scenario unfolded on Sunday, when an attacker exploited a vulnerability in Hyperbridge's cross-chain gateway, which connects various blockchains, to mint 1 billion Polkadot tokens, valued at $1.19 billion, on the Ethereum network, and then sold them for roughly $237,000 worth of ether. This exploit joins a growing list of bridge vulnerabilities in 2026, including a $270 million Drift Protocol hack on Solana last month, and highlights the ongoing issue of compromised infrastructure.
The attack targeted the bridge contract, rather than Polkadot's core network, and the native DOT token remained unaffected. The vulnerability stemmed from the way Hyperbridge's EthereumHost contract validated incoming cross-chain messages before passing them to the TokenGateway. Bridges, which facilitate the transfer of coins between different blockchains, remain a weak point 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.
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, instead storing an all-zeros commitment value, 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, allowing the attacker to execute changeAdmin on the bridged Polkadot token contract and transfer admin rights to their address. With administrative 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 approximately 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. Typically, weak liquidity is a major issue for large traders, but in this case, it helped minimize the attacker's gains, as the 1 billion tokens overwhelmed the available liquidity, resulting in the attacker receiving only a fraction of a cent per token.
If the vulnerability had been exploited on a deeper pool or a higher-value bridged asset, the losses would have been significantly larger. As of Monday morning, DOT was trading at just under $1.20.
CertiK identified the exploit, confirming that the attack vector was the Hyperbridge gateway contract and that the attacker profited around $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 attack vector.