zkLink was attacked due to a transient storage vulnerability, resulting in a loss of approximately 783,000 USD

According to an analysis by the Slow Mist security team, the cross-chain protocol zkLink was attacked, resulting in a loss of approximately $783,000.

The attacker used residual verification values in transient storage to forge the batch root required for withdrawal verification, subsequently completing 12 withdrawals, including 1 ETH withdrawal and 11 ERC-20 token withdrawals.

The attacker first claimed and wrote the verification value through a real cross-chain message, then reused that value in subsequent calls of the same transaction, leveraging the relay and gateway contracts to write the forged batch root.

The relevant contracts allow relayers to specify external call targets and parameters, and the verification value was not cleared or bound to the current call; the batch root update only verifies the gateway identity, lacking independent proof verification.