Cryptocurrency hacks have become all too familiar, but instances where attackers take substantial risks only to reap minimal rewards are rare. One such unusual case occurred on Sunday. An attacker leveraged a vulnerability in Hyperbridge's cross-chain gateway, which connects various 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 joins a growing list of bridge vulnerabilities in 2026, including a $270 million Drift Protocol incident on Solana last month.
The Sunday attack targeted the bridge contract, leaving Polkadot's core network and its native DOT token unaffected. The vulnerability stemmed from how Hyperbridge's EthereumHost contract validated incoming cross-chain messages before passing them to the TokenGateway. Bridges, designed to 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 empower an attacker to mint an unlimited supply of tokens.
The attack unfolded with the attacker submitting 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 either absent or circumventable proof validation for this specific call path. The gateway processed the message as legitimate, leading to the execution of changeAdmin on the bridged Polkadot token contract, thereby 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. 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 attack vector.