While cryptocurrency hacks are a common occurrence, it's unusual for attackers to take significant risks and end up with relatively modest gains. Such a scenario unfolded on Sunday, when an attacker exploited a vulnerability in Hyperbridge's cross-chain gateway, which connects different blockchains, to mint 1 billion Polkadot tokens on Ethereum and sell them for around $237,000 worth of ether. This exploit is the latest in a series of bridge vulnerabilities in 2026, including a $270 million Drift Protocol drain on Solana last month.
The attack targeted the bridge contract, not Polkadot's core network, and the native token DOT was not affected. The vulnerability lay in how Hyperbridge's EthereumHost contract validated incoming cross-chain messages before passing them to the TokenGateway. Bridges, which facilitate the transfer of coins between blockchains, are often the weakest link in cross-chain architecture, as they hold admin-level control over token contracts on destination chains, making them vulnerable to validation failures that can grant attackers unlimited supply. The attack began when the attacker submitted a forged message via dispatchIncoming, which was routed to TokenGateway.onAccept.
The request receipts check, which should have verified the message against a valid cross-chain state commitment from Polkadot, stored an all-zeros commitment value, suggesting 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. On a deeper pool or a higher-value bridged asset, the same vulnerability would have led to significantly larger losses.
As of Monday morning, DOT was trading just under $1.20. CertiK flagged 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.