SlowMist: The Core Issue of Usual Protocol's Hack Stems from the Usual Vault System

According to SlowMist monitoring, the Usual protocol suffered a complex arbitrage attack. Analysis shows that the attacker exploited the price difference between the protocol's internal mechanism and the external market. The core issue stemmed from the Usual Vault system, which allows USD0++ and USD0 tokens to be exchanged at a fixed 1:1 ratio, yet these same tokens trade at different prices on external decentralized exchanges. The attacker cleverly created a custom liquidity pool and manipulated the trading path, causing the Vault to release USD0 tokens without receiving the expected sUSDS collateral. Subsequently, the attacker sold the acquired USD0 tokens on the external market at a price higher than the internal exchange rate, thereby gaining arbitrage profits.