Cryptocurrency hacks are a common occurrence, but instances where attackers take significant risks only to gain minimal rewards are rare. One such incident occurred on Sunday, where 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 worth of ether.
This incident is the latest in a series of bridge vulnerabilities that have been discovered in 2026, including a $270 million drain on 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 way Hyperbridge's EthereumHost contract validated incoming cross-chain messages before passing them to the TokenGateway. Bridges are a crucial component in cross-chain architecture, enabling the transfer of coins between different blockchains, but they remain the weakest link due to their admin-level control over token contracts on destination chains. A single validation failure can grant an attacker unlimited supply, making them a prime target. The attack unfolded when the attacker submitted a forged message via dispatchIncoming, which was then routed to TokenGateway.onAccept.
The request receipts check failed to verify the message against a valid cross-chain state commitment from Polkadot, and 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 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. On a deeper pool or a higher-value bridged asset, the same vulnerability would have produced significantly larger losses. As of Monday morning, DOT was trading just under $1.20. The exploit was flagged by CertiK, which confirmed 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.