Cryptocurrency hacks have become commonplace, but instances where attackers take significant risks only to gain minimal rewards are rare. One such instance occurred recently. An attacker leveraged a vulnerability in the Hyperbridge cross-chain gateway, which links various 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 incident on Solana last month. The attack targeted the bridge contract, leaving Polkadot's core network and its native token DOT unaffected. The vulnerability stemmed from the EthereumHost contract's validation process for incoming cross-chain messages before they were passed to the TokenGateway.

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. A single validation failure can grant an attacker unlimited supply.

The attack unfolded when the attacker submitted a forged message via dispatchIncoming, which was then routed to TokenGateway.onAccept. The request receipts check, intended to verify 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 could be circumvented for this specific call path. The gateway processed the message as legitimate.

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 funneled them through Odos Router V3 into a Uniswap V4 DOT-ETH pool, extracting roughly 108.2 ETH across multiple swaps at slightly different prices.

However, the attacker's profit was capped due to weak liquidity in the bridged DOT pool on Ethereum. 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 with a higher-value bridged asset, the same vulnerability could have led to significantly larger losses. As of Monday morning, DOT was trading just under $1.20.

The exploit was flagged by CertiK, which confirmed 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.