While cryptocurrency hacks are commonplace, instances where attackers take significant risks only to gain minimal rewards are rare. Such a scenario unfolded on Sunday, as an attacker exploited a vulnerability in Hyperbridge's cross-chain gateway, which connects various blockchains, resulting in the minting of 1 billion Polkadot tokens on Ethereum, valued at $1.19 billion, and subsequently selling them for roughly $237,000 in ether.
This exploit contributes to the growing list of bridge vulnerabilities in 2026, following a $270 million Drift Protocol breach on Solana last month. The Sunday attack targeted the bridge contract, rather than Polkadot's core network, leaving the native DOT token unaffected. The vulnerability stemmed from 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 admin-level control over token contracts on destination chains, making them susceptible to attacks that can grant unlimited token supply. The exploit occurred 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, allowing the gateway to process the message as legitimate. This resulted in the execution of changeAdmin on the bridged Polkadot token contract, transferring admin rights to the attacker's address. With admin control, the attacker minted 1 billion tokens and sold them through Odos Router V3 into a Uniswap V4 DOT-ETH pool, extracting approximately 108.2 ETH across multiple swaps.
The limited liquidity of the bridged DOT pool on Ethereum worked against the attacker, capping their profit. The attacker's gain was significantly lower than expected due to the overwhelming of available liquidity, resulting in a fraction of a cent per token.
The same vulnerability could have led to more substantial losses if it had occurred on a deeper pool or a higher-value bridged asset. As of Monday morning, DOT trades just under $1.20. CertiK identified the exploit, confirming the attack vector was the Hyperbridge gateway contract and the attacker's profit of 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.