Attacker Exploits Vulnerability to Mint $1 Billion in Polkadot Tokens, but Only Manages to Steal $250,000

While cryptocurrency hacks are common, instances where attackers take substantial risks only to gain minimal rewards are rare. Such a scenario occurred on Sunday when an attacker exploited a vulnerability in Hyperbridge's cross-chain gateway, which connects multiple blockchains.

The attacker successfully minted 1 billion Polkadot tokens, valued at $1.19 billion, on the Ethereum network and subsequently sold them for approximately $237,000 worth of ether. This incident highlights the ongoing issue of bridge vulnerabilities in 2026, following a $270 million Drift Protocol exploit on Solana last month. The Sunday attack targeted the bridge contract, rather than Polkadot's core network, and the native DOT token remained unaffected. The vulnerability stemmed from the validation process of incoming cross-chain messages in Hyperbridge's EthereumHost contract.

Bridges, which facilitate the transfer of coins between 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 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, instead storing an all-zeros commitment value. This allowed the gateway to process the message as legitimate. The accepted message executed a changeAdmin function on the bridged Polkadot token contract, transferring administrative rights to the attacker's address.

With this 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 across multiple swaps. The limited liquidity in the bridged DOT pool on Ethereum worked against the attacker, capping their profit. If the same vulnerability were to be 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 below $1.20.

CertiK identified the exploit, confirming the attack vector was the Hyperbridge gateway contract, and the attacker's profit was 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.