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

Cryptocurrency hacks have become all too familiar, but instances where attackers take significant risks only to gain minimal rewards are unusual. Such a scenario unfolded on Sunday when an attacker leveraged a vulnerability in Hyperbridge's cross-chain gateway, which connects disparate blockchains. The attacker successfully minted 1 billion Polkadot tokens, valued at $1.19 billion, on the Ethereum network and then sold them for approximately $237,000 in ether.

This exploit joins a growing list of bridge vulnerabilities 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 the bridge contract and not Polkadot's core network, leaving the native DOT token unaffected.

The vulnerability was found in how Hyperbridge's EthereumHost contract validates incoming cross-chain messages before passing them to the TokenGateway. Bridges, which facilitate the movement of coins between blockchains, remain a weak point 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.

However, the request receipts check failed to verify the message against a valid cross-chain state commitment from Polkadot, instead storing an all-zeros commitment value, suggesting either absent or circumventable proof validation for this specific call path. The gateway processed the message as legitimate, leading to the execution of 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 sent them through Odos Router V3 into a Uniswap V4 DOT-ETH pool, extracting roughly 108.2 ETH across multiple swaps at slightly different prices. The limited liquidity in the bridged DOT pool on Ethereum worked against the attacker, capping their profit. The pool's limited 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 would 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 yet to publicly comment on the exploit or disclose whether other bridged token contracts using the same gateway are vulnerable to the same forged-message attack vector.