BlockSec has identified a critical vulnerability in closed-source contracts, leading to significant losses for SwapNet and Aperture Finance. The security firm reported that attackers exploited arbitrary call vulnerabilities in contracts on Ethereum, Arbitrum, Base, and BSC, resulting in over $17 million in losses. The flaw stemmed from insufficient input validation, allowing attackers to misuse token approvals and execute unauthorized asset transfers. The incidents, affecting different protocols and blockchains, highlight a common issue: user-controlled low-level calls and inadequate input validation in contracts with token approvals. This vulnerability underscores the importance of rigorous security measures in smart contract development to prevent similar exploits.