Cryptocurrency hacks have become all too common, but instances where attackers take significant risks only to reap relatively small rewards are rare. One such case occurred on Sunday. An attacker exploited a weakness in Hyperbridge's cross-chain gateway, connecting 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 incident is the latest in a series of bridge vulnerabilities that have come to light in 2026, including a $270 million Drift Protocol exploit on Solana last month, and a social engineering attack that involved compromised infrastructure.
The Sunday attack targeted the bridge contract rather than Polkadot's core network, leaving the native DOT token unaffected. The vulnerability was found in 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 unfolded 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 that 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 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 approximately 108.2 ETH across multiple swaps. However, the attacker's profits were limited due to weak liquidity in the bridged DOT pool on Ethereum, which was overwhelmed by the large number of tokens, resulting in the attacker receiving only a fraction of a cent per token.
If the same 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 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.