While cryptocurrency hacks are not uncommon, it is rare for attackers to take significant risks and end up with relatively minor gains. This unusual scenario unfolded on Sunday when an attacker exploited a vulnerability in Hyperbridge's cross-chain gateway, which connects various blockchains, to mint 1 billion Polkadot tokens, valued at $1.19 billion, on the Ethereum network, and then sold them for approximately $237,000 in ether. This exploit is the latest in a series of bridge vulnerabilities that have been exposed in 2026, including a $270 million drain on Solana's Drift Protocol last month and a social engineering attack that compromised infrastructure.

The attack on Sunday targeted the bridge contract, not Polkadot's core network, and the native DOT token was unaffected. The vulnerability was found in how Hyperbridge's EthereumHost contract validates incoming cross-chain messages before passing them to the TokenGateway.

Bridges, which facilitate the transfer of coins between different blockchains, remain a weak point in cross-chain architecture due to their admin-level control over token contracts on destination chains. 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.

However, 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, suggesting 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 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 then routed them through Odos Router V3 into a Uniswap V4 DOT-ETH pool, ultimately extracting around 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.

If the same vulnerability had 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. CertiK identified 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.