Cryptocurrency hacks are a common occurrence, but instances where attackers take significant risks only to gain minimal rewards are rare. Such a scenario unfolded on Sunday when an attacker exploited a weakness in Hyperbridge's cross-chain gateway, connecting 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 incident contributes to the growing list of vulnerabilities in bridge protocols in 2026, following a $270 million drain from Drift Protocol on Solana last month, as well as a social engineering attack that compromised infrastructure. The exploit targeted the bridge contract, leaving Polkadot's core network and its native token DOT unaffected.
The vulnerability was found 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 link in cross-chain architecture due to their administrative control over token contracts on destination chains, making them susceptible to attacks that can grant unlimited supply control with a single validation failure. The attack unfolded with the submission of 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, contained 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 executed a changeAdmin function 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 roughly 108.2 ETH across multiple swaps at slightly different prices.
However, the limited liquidity in 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.
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 trades 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 not publicly commented on the exploit or disclosed whether other bridged token contracts using the same gateway are vulnerable to the same forged-message attack vector.