Attacker Exploits Hyperbridge Vulnerability, Mints $1 Billion in Polkadot Tokens but Only Profits $250,000

Cryptocurrency hacks have become increasingly common, but instances where attackers take substantial risks only to gain minimal profits are rare. Such a scenario unfolded recently.

An attacker identified a vulnerability in Hyperbridge's cross-chain gateway, which connects various blockchains, and proceeded to mint 1 billion Polkadot tokens, valued at $1.19 billion, on the Ethereum network. However, the attacker only managed to sell these tokens for approximately $237,000 worth of ether. This exploit highlights the ongoing issue of bridge vulnerabilities in 2026, following a $270 million Drift Protocol incident on Solana last month.

The attack targeted the bridge contract rather than Polkadot's core network, and the native DOT token remained unaffected. The vulnerability stemmed from the EthereumHost contract's validation process for incoming cross-chain messages.

Bridges, which facilitate the transfer of coins between 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 with the submission of 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, allowing the gateway to process 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 and sold them through Odos Router V3 into a Uniswap V4 DOT-ETH pool, extracting roughly 108.2 ETH. However, the limited liquidity of the bridged DOT pool on Ethereum worked against the attacker, capping their profit. The bridged DOT 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 with a higher-value bridged asset, the same vulnerability could have led to significantly larger losses. 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 attack vector.