Cryptocurrency hacks have become increasingly common, but instances where attackers take substantial risks only to gain minimal rewards are rare. One such instance occurred on Sunday, where an attacker exploited a weakness in Hyperbridge's cross-chain gateway, which connects various blockchains, and minted 1 billion Polkadot tokens, valued at $1.19 billion, on the Ethereum network. The attacker then sold these tokens for approximately $237,000 in ether.
This exploit is the latest in a series of bridge vulnerabilities that have been uncovered in 2026, including a $270 million drain on Solana's Drift Protocol last month. The Sunday attack targeted the bridge contract rather than Polkadot's core network, leaving the native DOT token unaffected. The vulnerability was found in the validation process of incoming cross-chain messages by Hyperbridge's EthereumHost contract 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 administrative control over token contracts on destination chains. A single validation failure can grant an attacker unlimited minting capabilities.
The attack began when the attacker submitted a forged message via dispatchIncoming, which was then routed to TokenGateway.onAccept. However, the request receipts check failed to verify the message against a valid cross-chain state commitment from Polkadot, as it stored an all-zeros commitment value, indicating either the absence or circumvention of proof validation for this specific call path. Consequently, the gateway processed the message as legitimate, allowing the attacker to execute changeAdmin on the bridged Polkadot token contract and transfer admin rights to their address. With administrative control, the attacker minted 1 billion tokens in a single transaction and transferred them to a Uniswap V4 DOT-ETH pool via Odos Router V3, ultimately extracting around 108.2 ETH across multiple swaps at varying prices.
The limited liquidity of the bridged DOT pool on Ethereum worked against the attacker, capping their profit. Typically, weak liquidity is a significant issue for large traders, but in this case, it hindered the attacker's ability to capitalize on the exploit.
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 greater.
As of Monday morning, DOT was trading just below $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 yet to publicly comment on the exploit or disclose whether other bridged token contracts using the same gateway are vulnerable to the same attack vector.