While cryptocurrency hacks are a common occurrence, it's rare for attackers to take significant risks and end up with relatively modest gains. However, this unusual scenario unfolded on Sunday when an attacker exploited a vulnerability in the Hyperbridge cross-chain gateway, which connects different blockchains. The attacker successfully minted 1 billion Polkadot tokens, valued at $1.19 billion, on the Ethereum network and then sold them for approximately $237,000 worth of ether. This incident is the latest in a series of bridge vulnerabilities that have been exposed in 2026, including a $270 million exploit on the Solana network last month.
The attack on Sunday targeted the bridge contract, rather than Polkadot's core network, and the native DOT token remained unaffected. The vulnerability was found in how the Hyperbridge EthereumHost contract validated incoming cross-chain messages before passing them to the TokenGateway. Bridges, which facilitate the transfer 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 that a single validation failure can grant an attacker the ability to mint an unlimited supply of tokens.
An analysis of the attack reveals that the attacker submitted a forged message via the dispatchIncoming function, which was then routed to the TokenGateway.onAccept function. 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, indicating that the proof validation was either absent or could be circumvented for this specific call path. As a result, the gateway processed the message as legitimate.
The accepted message then executed the changeAdmin function 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 routed them through the 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 limited 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 vulnerability had been exploited on a deeper pool or a higher-value bridged asset, the losses would have been significantly larger.
The price of DOT was trading just under $1.20 during Asian morning hours on Monday. The security firm 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 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.