SlowMist Introduces xToken Hack Event Analysis

According to the SlowMist Zone report, the Ethereum DeFi xToken project has been under attack, resulting in a loss of around $ 25 million, and the review by SlowMist's security team is as follows: The two modules hacked this time are the xBNTa contract and the xSNXa contract on xToken. Both deals were marred by "counterfeit trade" attacks and oracle attacks, respectively. 1) xBNTa contract against analysis 1. The xBNTa deal contains a mint feature that allows users to trade ETH into BNT using Bancor Netowrk and exchange coins based on the exchange rate provided by the Bancor network. 2. There is a different way in the mint function used to convert ETH to BNT through the Bancor network, but the cost of the method can be passed on by the user. 3. Since the attacker is crossing a forged path, the xBNTa contract uses the previous attacker's method to exchange tokens in order to achieve the objective of exchanging coins using different pairs. The contract itself fulfills the unreliable advertising purpose, going beyond the limits that ETH / BNT trading partners are required to use for trading. 2) xSNXa contract against analysis 1. The xSNXa deal contains a special mint that allows users to transfer ETH to xSNX using the Kyber Network compiler exchange. 2. By controlling the price of the ETH / SNX trading partner in the Lightning Uniswap loan, the attacker can intercept the reports of the SNX / ETH trading partner and then intercept the quotes on the Kyber network. Therefore, this affects the value obtained from the xSNXa contract. 3. The opponent uses the amount of checks to give coins to reach the goal of the strike.