While cryptocurrency hacks are commonplace, instances where attackers take significant risks only to reap modest rewards are rare. Such a scenario unfolded on Sunday, as an attacker exploited a vulnerability in Hyperbridge's cross-chain gateway, which connects disparate blockchains, to mint 1 billion Polkadot tokens, valued at $1.19 billion, on the Ethereum network, and subsequently sold them for approximately $237,000 in ether.
This exploit adds to the growing list of bridge vulnerabilities in 2026, including the $270 million Drift Protocol incident on Solana last month. The attack targeted Hyperbridge's EthereumHost contract, specifically the validation process for incoming cross-chain messages, rather than Polkadot's core network, leaving the native DOT token unaffected. The vulnerability stemmed from the contract's failure to properly verify the legitimacy of cross-chain messages before passing them to the TokenGateway, allowing the attacker to submit a forged message that granted them admin control over the bridged Polkadot token contract.
Bridges, which facilitate the transfer of coins between blockchains, remain a weak point in cross-chain architecture due to their admin-level control over token contracts on destination chains. The attack unfolded when the attacker submitted 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, instead storing an all-zeros commitment value, suggesting that proof validation was either absent or circumventable for this specific call path. 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 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. Notably, the limited liquidity of the bridged DOT pool on Ethereum worked against the attacker, capping their profit.
The pool's shallow 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 traded 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.