Publication Date


Date of Final Oral Examination (Defense)


Type of Culminating Activity


Degree Title

Master of Science in Computer Science


Computer Science

Major Advisor

Jidong Xiao, Ph.D.


Catherine Olschanowsky, Ph.D.


Amit Jain, Ph.D.


Virtualized cloud computing services are a crucial facet in the software industry today, with clear evidence of its usage quickly accelerating. Market research forecasts an increase in cloud workloads by more than triple, 3.3-fold, from 2014 to 2019 [33]. Integrating system security is then an intrinsic concern of cloud platform system administrators that with the growth of cloud usage, is becoming increasingly relevant. People working in the cloud demand security more than ever. In this paper, we take an offensive, malicious approach at targeting such cloud environments as we hope both cloud platform system administrators and software developers of these infrastructures can advance their system securities.

A vulnerability could exist in any layer of a computer system. It is commonly believed in the security community that the battle between attackers and defenders is determined by which side can exploit these vulnerabilities and then gain control at the lower layer of a system [22]. Because of this perception, kernel level defense is proposed to defend against user-level malware [25], hypervisor-level defense is proposed to detect kernel-level malware or rootkits [36, 47, 41], hardware-level defense is proposed to defend or protect hypervisors [4, 51, 45].

Once attackers find a way to exploit a particular vulnerability and obtain a certain level of control over the victim system, retaining that control and avoiding detection becomes their top priority. To achieve this goal, various rootkits have been developed. However, existing rootkits have a common weakness: they are still detectable as long as defenders can gain control at a lower-level, such as the operating system level, the hypervisor level, or the hardware level. In this paper, we present a new type of rootkit called CloudSkulk, which is a nested virtual machine (VM) based rootkit. While nested virtualization has attracted sufficient attention from the security and cloud community, to the best of our knowledge, we are the first to reveal and demonstrate nested virtualization can be used by attackers for developing malicious rootkits. By impersonating the original hypervisor to communicate with the original guest operating system (OS) and impersonating the original guest OS to communicate with the hypervisor, CloudSkulk is hard to detect, regardless of whether defenders are at the lower-level (e.g., in the original hypervisor) or at the higher-level (e.g., in the original guest OS).

We perform a variety of performance experiments to evaluate how stealthy the proposed rootkit is at remaining unnoticed as introducing one more layer of virtualization inevitably incurs extra overhead. Our performance characterization data shows that an installation of our novel rootkit on a targeted nested virtualization environment is likely to remain undetected unless the guest user performs IO intensive-type workloads.


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