ONIS: Inferring TCP/IP-based Trust Relationships Completely Off-Path

Xu Zhang University of New Mexico, USA
Jeffrey Knockel University of New Mexico, USA
Jedidiah Crandall University of New Mexico, USA


We present ONIS, a new scanning technique that can perform network measurements such as: inferring TCP/IP-based trust relationships off-path, stealthily port scanning a target without using the scanner's IP address, detecting off-path packet drops between two international hosts. These tasks typically rely on a core technique called the idle scan, which is a special kind of port scan that appears to come from a third machine called a zombie. The scanner learns the target's status from the zombie by using its TCP/IP side channels. Unfortunately, the idle scan assumes that the zombie has IP identifiers (IPIDs) which exhibit the now-discouraged behavior of being globally incrementing. The use of this kind of IPID counter is becoming increasingly rare in practice. Our technique, unlike the idle scan, is based on a much more advanced IPID generation scheme, that of the prevalent Linux kernel. Although Linux's IPID generation scheme is specifically intended to reduce information flow, we show that using Linux machines as zombies in an indirect scan is still possible. ONIS has 87% accuracy, which is comparable to nmap's implementation of the idle scan at 86%. ONIS's much broader choice of zombies will enable it to be a widely used technique which can fulfill various network measurement tasks.

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