Attacker Exploits Vulnerability to Mint $1 Billion in Polkadot Tokens, But Only Manages to Steal $250,000

While cryptocurrency hacks are becoming increasingly common, instances where attackers take significant risks only to walk away with minimal gains are rare. Such a scenario unfolded on Sunday when an attacker exploited a vulnerability in Hyperbridge's cross-chain gateway, which connects different blockchains.

The attacker successfully minted 1 billion Polkadot tokens, valued at $1.19 billion, on the Ethereum network and sold them for approximately $237,000 worth of 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 how Hyperbridge's EthereumHost contract validated incoming cross-chain messages before passing them to the TokenGateway.

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 when the attacker submitted a forged message via dispatchIncoming, which was 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 administrative rights to the attacker's address. With administrative 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 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 could have produced significantly larger losses.

As of Monday morning, DOT was trading just under $1.20. CertiK confirmed 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.