While cryptocurrency hacks are common, instances where attackers take significant risks only to gain minimal rewards are rare. Such a scenario unfolded on Sunday when an attacker exploited a vulnerability in the Hyperbridge cross-chain gateway, which connects various blockchains. The attacker successfully minted 1 billion Polkadot tokens, valued at $1.19 billion, on the Ethereum network and sold them for roughly $237,000 in ether.
This incident is the latest in a series of bridge vulnerabilities that have been exposed in 2026, including a $270 million exploit of the Drift Protocol on Solana last month. The attack on Sunday targeted the bridge contract and not the core Polkadot network, with the native DOT token remaining unaffected. The vulnerability was found in the way the Hyperbridge EthereumHost contract validates incoming cross-chain messages before passing them to the TokenGateway. Cross-chain bridges, which facilitate the transfer of coins between different blockchains, are often the weakest link in cross-chain architecture due to their administrative control over token contracts on destination chains.
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, and instead stored an all-zeros commitment value. This allowed the gateway to process the message as legitimate. The accepted message then executed changeAdmin on the bridged Polkadot token contract, transferring administrative rights to the attacker's address. With administrative 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 at different prices.
The limited liquidity of the bridged DOT pool on Ethereum worked against the attacker, capping their profit. The pool's weak depth meant that the 1 billion tokens overwhelmed the available liquidity, 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 and confirmed that the attack vector was the Hyperbridge gateway contract, with the attacker profiting 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 attack vector.