Attacker Exploits Cross-Chain Vulnerability, Mints $1 Billion in Polkadot Tokens but Only Gains $250,000

Cryptocurrency hacks have become increasingly common, but instances where attackers take significant risks and end up with relatively minor gains are rare. Such a scenario unfolded on Sunday when an attacker exploited a vulnerability in the Hyperbridge cross-chain gateway, which connects different blockchain networks.

The attacker successfully minted 1 billion Polkadot tokens, valued at approximately $1.19 billion, on the Ethereum network and sold them for around $237,000 worth of ether. This exploit highlights the ongoing issue of bridge vulnerabilities in 2026, following a $270 million drain on the Drift Protocol on Solana last month.

The attack targeted the bridge contract, rather than Polkadot's core network, and the native DOT token remained unaffected. The vulnerability lay in the validation process of incoming cross-chain messages by Hyperbridge's EthereumHost contract before passing them to the TokenGateway.

Bridges, which facilitate the transfer of coins between blockchain networks, are often 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 unlimited supply.

The attack began with the submission of 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, allowing the gateway to process the message as legitimate. This resulted in the transfer of admin rights to the attacker's address, enabling them to mint 1 billion tokens in a single transaction. The attacker then routed these tokens through Odos Router V3 into a Uniswap V4 DOT-ETH pool, extracting around 108.2 ETH across multiple swaps at varying prices.

The limited liquidity in the bridged DOT pool on Ethereum worked against the attacker, capping their profit. If the same vulnerability had been exploited on a deeper pool or a higher-value bridged asset, the losses would have been significantly greater. The price of DOT stood at just under $1.20 as of Monday morning. 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.