Attacker Exploits Cross-Chain Vulnerability, Mints $1 Billion in Polkadot Tokens but Only Nets $250,000

While crypto hacks are a common occurrence, instances where attackers take significant risks only to reap relatively small rewards are rare. Such an unusual scenario unfolded on Sunday when an attacker leveraged a vulnerability in Hyperbridge's cross-chain gateway to mint 1 billion Polkadot tokens, valued at $1.19 billion, on the Ethereum network and subsequently sold them for approximately $237,000 in ether. This exploit highlights the growing list of bridge vulnerabilities in 2026, following a $270 million drain on Solana's Drift Protocol last month. The attack targeted the bridge contract rather than Polkadot's core network, leaving the native DOT token 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 different blockchains, remain a weak point 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 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, allowing the gateway to process the message as legitimate. This led to the execution of changeAdmin on the bridged Polkadot token contract, transferring admin rights to the attacker's address. With administrative 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.

Notably, the limited liquidity in the bridged DOT pool worked against the attacker, capping their profits. The same vulnerability could have resulted in significantly larger losses if the pool had greater depth or if the bridged asset had a higher value. As of Monday morning, DOT was trading just under $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 not publicly addressed the exploit or disclosed whether other bridged token contracts using the same gateway are vulnerable to similar attacks.