SlowMist: zkLink Hacked, Lost Approximately $783,000 Involving Transient Storage Vulnerability

TechFlow reported that on October 31, according to an analysis by the SlowMist Security Team, the cross-chain protocol zkLink was attacked on October 29, resulting in losses of approximately $783,000. The attacker exploited residual verification values in transient storage to forge batch roots used for withdrawal verification, and subsequently completed 12 withdrawals, including 1 ETH withdrawal and 11 ERC-20 token withdrawals.

The analysis indicates that the attacker first obtained and wrote a verification value via a legitimate cross-chain message, then reused this value in subsequent calls within the same transaction to write a forged batch root through relay and gateway contracts. The relevant contracts allow relayers to specify external call targets and parameters, but verification values are not cleared or bound to the current call, while batch root updates only verify the gateway's identity, lacking independent proof verification.