While cryptocurrency hacks are commonplace, instances where attackers assume significant risks only to gain minimal rewards are rare. Such an unusual scenario unfolded on Sunday when an attacker leveraged a vulnerability in the Hyperbridge cross-chain gateway, which connects multiple blockchains, to mint 1 billion Polkadot tokens, valued at $1.19 billion, on the Ethereum network, and subsequently sold them for around $237,000 in ether. This exploit contributes to the growing list of bridge vulnerabilities in 2026, including the $270 million Drift Protocol hack on Solana last month, and a social engineering attack that compromised infrastructure.
The attack targeted the bridge contract rather than Polkadot's core network, leaving the native DOT token 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.
Cross-chain bridges, which facilitate the transfer of coins between different blockchains, remain a weak point in cross-chain architecture due to their administrative control over token contracts on destination chains. This means a single validation failure can grant an attacker unlimited supply. The attack began when the attacker submitted 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, instead storing an all-zeros commitment value, suggesting the proof validation was either absent or circumventable.
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 and sold them through Odos Router V3 into a Uniswap V4 DOT-ETH pool, earning approximately 108.2 ETH. However, the limited liquidity of the bridged DOT pool on Ethereum worked against the attacker, capping their profits. The pool's limited depth meant the 1 billion tokens overwhelmed the available liquidity, resulting in the attacker receiving only a fraction of a cent per token.
In a deeper pool or with 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 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.