Attacker Exploits Hyperbridge Vulnerability, Steals $250,000 Despite Minting $1 Billion in Polkadot Tokens

While cryptocurrency hacks are common, it's unusual for attackers to take significant risks and end up with relatively minor gains. This rare scenario occurred on Sunday when an attacker exploited a vulnerability in Hyperbridge's cross-chain gateway, connecting various blockchains, and minted 1 billion Polkadot tokens, valued at $1.19 billion, on Ethereum. The attacker then sold these tokens for around $237,000 in ether. This incident is the latest in a series of bridge vulnerabilities in 2026, including a $270 million exploit on Solana's Drift Protocol last month.

The targeted bridge contract, rather than Polkadot's core network, was the weak point, with the native DOT token remaining unaffected. The vulnerability stemmed from the validation process of incoming cross-chain messages in Hyperbridge's EthereumHost contract before they were passed to the TokenGateway. Cross-chain bridges, which facilitate the transfer of coins between blockchains, are often the weakest link due to their admin-level control over token contracts on destination chains. A single validation failure can grant an attacker unlimited minting capabilities.

The attack involved the submission of a forged message via dispatchIncoming, which was 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. This resulted in the execution of changeAdmin, 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 approximately 108.2 ETH.

However, the limited liquidity in the bridged DOT pool on Ethereum meant that the attacker received only a fraction of a cent per token, capping their profit. The lack of depth in the market worked against the attacker, a situation that would have resulted in significantly larger losses if the pool had been deeper or the bridged asset more valuable.

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, resulting in the attacker profiting around $237,000 from minting and selling the bridged tokens.

Hyperbridge has yet to publicly address the exploit or disclose whether other bridged token contracts using the same gateway are vulnerable to similar attacks.