Cryptocurrency hacks have become all too familiar, but it's rare for attackers to take significant risks only to end up with relatively modest gains. However, this unusual scenario unfolded on a recent Sunday. An attacker discovered a vulnerability in the Hyperbridge cross-chain gateway, which connects various blockchains, and exploited it to mint 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 incident is the latest in a series of bridge vulnerabilities that have been exposed in 2026, including a $270 million exploit on Solana's Drift Protocol last month. The Sunday attack targeted the bridge contract rather than Polkadot's core network, and the native DOT token remained unaffected. The weakness lay 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 because they hold admin-level control over token contracts on destination chains.

This means a single validation failure can grant an attacker unlimited supply. The attack began 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 instead stored an all-zeros commitment value. 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 around 108.2 ETH. However, the attacker's gains were limited due to weak liquidity in the market.

The bridged DOT pool on Ethereum had limited depth, which 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 at just under $1.20. CertiK identified the exploit and confirmed that the attack vector was the Hyperbridge gateway contract, with the attacker profiting 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.