Cryptocurrency hacks are a common occurrence, but instances where attackers take significant risks and end up with relatively small gains are rare. Such a scenario unfolded on Sunday, when an attacker exploited a vulnerability in Hyperbridge's cross-chain gateway, which connects different blockchain networks. The attacker successfully minted 1 billion Polkadot tokens, valued at $1.19 billion, on the Ethereum network and sold them for around $237,000 worth of ether. This incident highlights the growing concern of bridge vulnerabilities in 2026, following a $270 million exploit on Solana's Drift Protocol last month.
The Sunday attack targeted the bridge contract, rather than Polkadot's core network, and the native DOT token remained unaffected. The vulnerability stemmed from the way Hyperbridge's EthereumHost contract validated incoming cross-chain messages before passing them to the TokenGateway.
Bridges, which facilitate the transfer of coins between blockchain networks, are often the weakest link in cross-chain architecture due to their admin-level control over token contracts on destination chains. A single validation failure can grant an attacker the ability to mint an unlimited supply of tokens. The attack began when the hacker submitted 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, stored an all-zeros commitment value, indicating that the proof validation was either absent or circumventable for this specific call path.
As a result, the gateway processed the message as legitimate. The accepted message executed changeAdmin on the bridged Polkadot token contract, transferring admin rights to the attacker's address.
With admin 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 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. If the same vulnerability had been exploited on a deeper pool or a higher-value bridged asset, the losses would have been significantly larger.
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 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.