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

While cryptocurrency hacks are a common occurrence, instances where attackers take significant risks only to gain minimal rewards are rare. One such incident occurred on Sunday, where an attacker exploited a vulnerability in the Hyperbridge cross-chain gateway, which connects multiple blockchains. The attacker successfully minted 1 billion Polkadot tokens, valued at $1.19 billion, on the Ethereum network and subsequently sold them for approximately $237,000 in ether.

This exploit highlights the growing list of bridge vulnerabilities in 2026, following a $270 million Drift Protocol hack on Solana last month. The attack targeted the bridge contract, rather than Polkadot's core network, and the native DOT token remained unaffected.

The vulnerability was found in the EthereumHost contract's validation process for incoming cross-chain messages before they were passed to the TokenGateway. Bridges, which facilitate the transfer of coins between different blockchains, remain a weak point 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 unfolded when the attacker submitted 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. The accepted message granted the attacker admin rights to the bridged Polkadot token contract, enabling them to mint 1 billion tokens in a single transaction.

These tokens were then routed through Odos Router V3 into a Uniswap V4 DOT-ETH pool, from which the attacker extracted roughly 108.2 ETH across multiple swaps. However, 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 could have led to significantly larger losses. As of Monday morning, DOT was trading at just under $1.20. The exploit was flagged by CertiK, which confirmed 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 attack vector.