While cryptocurrency hacks are not unusual, it's rare for attackers to take significant risks and end up with relatively small gains. However, this unusual scenario unfolded on Sunday when an attacker exploited a vulnerability in Hyperbridge's cross-chain gateway, connecting various blockchains, and minted 1 billion Polkadot tokens, valued at $1.19 billion, on Ethereum, only to sell them for approximately $237,000 in ether. This incident is the latest in a string of bridge vulnerabilities in 2026, including a $270 million Drift Protocol exploit on Solana and a social engineering attack involving compromised infrastructure. The Sunday exploit targeted the bridge contract, not Polkadot's core network, and the native DOT token was unaffected.
The vulnerability lay in how Hyperbridge's EthereumHost contract validated incoming cross-chain messages before passing them to the TokenGateway. Bridges, which facilitate the transfer of coins between blockchains, remain the weakest link in cross-chain architecture due to their admin-level control over token contracts on destination chains. A single validation failure can grant an attacker the ability to mint an unlimited supply.
The attack began when the attacker submitted a forged message via dispatchIncoming, which was routed to TokenGateway.onAccept. The request receipts check, which should have verified the message against a valid cross-chain state commitment from Polkadot, stored an all-zeros commitment value, suggesting the proof validation was either absent or circumventable for this specific call path. The gateway processed the message as legitimate, and 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 routed 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 gain was limited due to weak liquidity in the bridged DOT pool on Ethereum, which was overwhelmed by the 1 billion tokens, 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 led to significantly larger losses. As of Monday morning, DOT was trading just under $1.20. CertiK flagged the exploit, confirming 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.