While cryptocurrency hacks are common, instances where attackers take significant risks only to gain minimal rewards are rare. Such a scenario occurred on Sunday when an attacker exploited a vulnerability in the Hyperbridge cross-chain gateway, connecting various blockchains, and minted 1 billion Polkadot tokens, valued at $1.19 billion, on the Ethereum network.
The attacker then sold these tokens for around $237,000 in ether. This exploit highlights the growing list of bridge vulnerabilities in 2026, including the $270 million Drift Protocol incident on Solana last month.
The 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 in Hyperbridge's EthereumHost contract before they were passed 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 validation failures that can grant attackers unlimited token minting capabilities. The attack unfolded when the perpetrator submitted 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, contained an all-zeros commitment value, indicating either the absence or circumvention of proof validation for this specific call path.
The gateway processed the message as legitimate, leading to the execution of changeAdmin on the bridged Polkadot token contract and transferring administrative 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 of 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 morning, DOT was trading just under $1.20. CertiK identified the exploit, confirming that the attack vector was the Hyperbridge gateway contract and that the attacker profited around $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 attack vector.