While cryptocurrency hacks are not uncommon, instances where attackers undertake significant risks only to gain relatively modest rewards are rare. Such a scenario unfolded on Sunday, when an attacker exploited a weakness in the Hyperbridge 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 worth of ether.
This exploit highlights the ongoing issue of bridge vulnerabilities in 2026, following a $270 million drain on Solana's Drift Protocol last month and a social engineering attack that compromised infrastructure. The attack targeted the bridge contract, rather than Polkadot's core network, with the native DOT token remaining 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 blockchains, remain a weak point in cross-chain architecture due to their administrative control over token contracts on destination chains, making them susceptible to attacks that can grant unlimited token minting capabilities with a single validation failure. The attack began with the submission of a forged message via dispatchIncoming, which was then routed to TokenGateway.onAccept. However, 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 the absence or circumvention of proof validation for this specific call path, leading 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 transferred them through Odos Router V3 into a Uniswap V4 DOT-ETH pool, extracting around 108.2 ETH across multiple swaps at slightly different prices.
The limited liquidity of the bridged DOT pool on Ethereum worked against the attacker, as 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's Asian morning hours, DOT was trading just under $1.20.
The exploit was flagged by CertiK, which confirmed the attack vector as the Hyperbridge gateway contract and estimated the attacker's profit at 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 forged-message attack vector.