🚨On April 13, 2026 at 03:55:23 UTC, a helper contract deployed by the attacker used Hyperbridge's
@hyperbridge Ethereum-side ISMP message path to deliver a forged governance-style PostRequest into TokenGateway through HandlerV1.handlePostRequests(...).
💡The exploit is best classified as an access-control failure at the proof-validation boundary. More specifically, HandlerV1 accepted a malicious cross-chain request as authentic because the attacker abused an index-handling flaw in the Merkle Mountain Range proof verifier: the forged request was submitted with a crafted leaf/proof combination that caused the verifier to accept the stored overlayRoot without actually binding the forged message commitment into the computed root. As a result, a fake request claiming to originate from Hyperbridge governance (POLKADOT-3367) passed validation and was dispatched downstream as trusted input.
Once delivered to TokenGateway, the forged payload was decoded as a ChangeAssetAdmin action for the bridged DOT asset. Since the gateway’s governance path trusted any request whose source matched host.hyperbridge(), it executed changeAdmin(...) on the ERC6160 DOT token and reassigned admin rights to the attacker helper. That immediately gave the helper effective mint authority, allowing it to mint 1,000,000,000 DOT, approve the Odos router, and dump the full balance through Odos / Uniswap v4 swap infrastructure for 108.206143512481490001 ETH, which was then forwarded back through the attacker’s contracts to the EOA.
👇More concrete vulnerable code snippets show below.