Cryptocurrency hacks have become commonplace, but instances where attackers take significant risks only to reap minimal rewards are rare. Such a scenario unfolded on Sunday when an attacker exploited a vulnerability in the Hyperbridge cross-chain gateway, which connects disparate blockchains, to mint 1 billion Polkadot tokens on Ethereum, valued at $1.19 billion, and subsequently sold them for approximately $237,000 in ether.
This exploit is the latest in a series of bridge vulnerabilities that have come to light in 2026, including a $270 million drain on the Drift Protocol in Solana last month and a social engineering attack that compromised infrastructure. The Sunday attack targeted the bridge contract, leaving Polkadot's core network and its native token DOT unaffected. The vulnerability stemmed from the EthereumHost contract's validation process for incoming cross-chain messages before passing them to the TokenGateway. Bridges, designed to facilitate the transfer of coins between blockchains, remain a weak link in cross-chain architecture due to their admin-level control over token contracts on destination chains, making them susceptible to validation failures that can grant attackers unlimited minting capabilities.
The attack began with the submission of 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, instead storing an all-zeros commitment value, indicating either the absence or circumvention of proof validation for this specific call path.
As a result, the gateway processed the message as legitimate, leading to the execution of changeAdmin on the bridged Polkadot token contract and transferring admin rights to the attacker's address. With admin control, the attacker minted 1 billion tokens in a single transaction and funneled them through Odos Router V3 into a Uniswap V4 DOT-ETH pool, extracting roughly 108.2 ETH across multiple swaps at slightly different prices.
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.
Had the vulnerability 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. The exploit was flagged by CertiK, which confirmed the attack vector as the Hyperbridge gateway contract and estimated the attacker's profit at 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 attack vector.