While cryptocurrency hacks are a common occurrence, it's rare for attackers to take enormous risks only to reap minimal rewards. This unusual scenario unfolded on Sunday, as an attacker leveraged a vulnerability in Hyperbridge's cross-chain gateway to mint 1 billion Polkadot tokens on Ethereum, valued at $1.19 billion, and subsequently sold them for approximately $237,000 in ether. This incident highlights the growing concerns surrounding bridge vulnerabilities in 2026, following a $270 million Drift Protocol exploit on Solana last month.
The vulnerability in question was specific to the bridge contract and did not affect Polkadot's core network or its native token, DOT. The issue arose from the way Hyperbridge's EthereumHost contract validated incoming cross-chain messages before passing them to the TokenGateway, allowing the attacker to bypass state proof validation and gain admin control over the bridged DOT token.
Bridges, which facilitate the transfer of coins between blockchains, remain a weak 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 minting capabilities. 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.
The accepted message executed a changeAdmin function 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 sold them through Odos Router V3 into a Uniswap V4 DOT-ETH pool, extracting roughly 108.2 ETH across multiple swaps at varying prices. The limited liquidity of 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 greater. 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 around $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.