While cryptocurrency hacks are not uncommon, instances where attackers take substantial risks only to gain minimal rewards are rare. Such a scenario unfolded on Sunday when an attacker exploited a vulnerability in Hyperbridge's cross-chain gateway, which connects various blockchains, resulting in the minting of 1 billion Polkadot tokens, valued at $1.19 billion, on the Ethereum network.
The attacker then sold these tokens for around $237,000 worth of ether. This incident adds to the growing list of bridge vulnerabilities in 2026, following a $270 million drain from the Drift Protocol on Solana last month. The exploit targeted the bridge contract and not Polkadot's core network, with the native DOT token remaining unaffected.
The vulnerability was found in the validation process of incoming cross-chain messages by Hyperbridge's EthereumHost contract before they were passed to the TokenGateway. Bridges, which facilitate the movement of coins between different blockchains, are often the weakest link in cross-chain architecture due to their admin-level control over token contracts on destination chains. This means a single validation failure can grant an attacker the ability to mint an unlimited supply of tokens.
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.
The gateway treated the message as legitimate, leading to the execution of changeAdmin on the bridged Polkadot token contract, thereby transferring admin rights to the attacker's address. With this 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 slightly different prices. The limited liquidity in 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 morning, DOT was trading just under $1.20. CertiK identified the exploit, confirming that the attack vector was indeed 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 type of forged-message attack.