Real-world Detection of Polymorphic Attacks

As state-of-the-art attack detection technology becomes more prevalent, attackers have started to employ evasion techniques such as code obfuscation and polymorphism to defeat existing defenses. We have recently proposed network-level emulation, a heuristic detection method that scans network traffic to detect polymorphic attacks. Our approach uses a CPU emulator to dynamically analyze every potential instruction sequence in the inspected traffic, aiming to identify the execution behavior of certain malicious code classes, such as self-decrypting polymorphic shellcode. In this paper, we present results and experiences from deployments of network-level emulation in production networks. After more than a year of continuous operation, our prototype implementation has captured more than a million attacks against real systems, while so far has not resulted to any false positives. The observed attacks employ a highly diverse set of exploits, often against less widely used vulnerable services, and in some cases, sophisticated obfuscation schemes.