Cryptocurrency hacks have become all too familiar, but instances where attackers take significant risks only to reap relatively meager rewards are rare. Such a scenario unfolded on Sunday when an attacker exploited a vulnerability in Hyperbridge's cross-chain bridge, which connects disparate blockchains, to mint 1 billion Polkadot tokens valued at $1.19 billion on Ethereum.
The attacker then sold these tokens for approximately $237,000 in ether. This exploit is the latest in a series of bridge vulnerabilities exposed in 2026, including a $270 million exploit on Solana's Drift Protocol last month and a social engineering attack that compromised infrastructure. The Sunday attack targeted Hyperbridge's bridge contract rather than Polkadot's core network, leaving the native DOT token unaffected. The vulnerability lay in how the EthereumHost contract validated incoming cross-chain messages before passing them to the TokenGateway.
Bridges, which facilitate the movement of coins between blockchains, remain the weakest link in cross-chain architecture due to their admin-level control over token contracts on destination chains. A single validation failure can grant an attacker unlimited supply. The attack began with the attacker submitting a forged message via dispatchIncoming, which was then routed to TokenGateway.onAccept. The request receipts check, designed to verify the message against a valid cross-chain state commitment from Polkadot, contained an all-zeros commitment value, suggesting that proof validation was either absent or could be circumvented for this specific call path.
The gateway processed the message as legitimate, leading to the execution of changeAdmin on the bridged Polkadot token contract, which transferred admin 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, ultimately extracting about 108.2 ETH across multiple swaps at slightly different prices. However, the limited liquidity of the bridged DOT pool on Ethereum worked against the attacker, capping their profit.
Normally, weak liquidity is a significant issue for large investors, but in this case, it limited the attacker's gains. The bridged DOT pool's limited depth meant that the 1 billion tokens overwhelmed 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 indeed the Hyperbridge gateway contract and that the attacker profited 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 the same attack vector.