TAO: Protecting Against Hitlist Worms Using Transparent Address Obfuscation

Sophisticated worms that use precomputed hitlists of vulnerable targets are especially hard to contain, since they are harder to detect, and spread at rates where even automated defenses may not be able to react in a timely fashion. Recent work has examined a proactive defense mechanism called Network Address Space Randomization (NASR) whose objective is to harden networks specifically against hitlist worms. The idea behind NASR is that hitlist information could be rendered stale if nodes are forced to frequently change their IP addresses. However, the originally proposed DHCP-based implementation may induce passive failures on hosts that change their addresses when connections are still in progress. The risk of such collateral damage also makes it harder to perform address changes at the timescales necessary for containing fast hitlist generators. In this paper we examine an alternative approach to NASR that allows both more aggressive address changes and also eliminates the problem of connection failures, at the expense of increased implementation and deployment cost. Rather than controlling address changes through a DHCP server, we explore the design and performance of transparent address obfuscation (TAO). In TAO, network elements transparently change the external address of internal hosts, while ensuring that existing connections on previously used addresses are preserved without any adverse consequences. In this paper we present the TAO approach in more detail and examine its performance.