Attacker Exploits Polkadot Token Vulnerability on Ethereum, Nets Only $250,000

While cryptocurrency hacks are commonplace, it's rare for attackers to take significant risks and end up with relatively modest gains. However, this unusual scenario unfolded on Sunday when an attacker exploited a vulnerability in the Hyperbridge cross-chain gateway, connecting various blockchains, and minted 1 billion Polkadot tokens, valued at $1.19 billion, on the Ethereum network.

The attacker then sold these tokens for approximately $237,000 in ether. This incident highlights the growing list of bridge vulnerabilities in 2026, including a $270 million Drift Protocol exploit on Solana last month.

The Sunday attack targeted the bridge contract, not 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 before passing them to the TokenGateway. Bridges, which facilitate the transfer of coins between blockchains, are often the weakest link in cross-chain architecture due to their admin-level control over token contracts on destination chains. This means 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. The request receipts check, intended to verify the message against a valid cross-chain state commitment from Polkadot, stored an all-zeros commitment value. This suggested that the proof validation was either absent or circumventable for this specific call path, 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 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. The limited liquidity in the bridged DOT pool on Ethereum worked against the attacker, capping their profit.

The pool's weak 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 not publicly commented on the exploit or disclosed whether other bridged token contracts using the same gateway are vulnerable to the same attack vector.