architecture, and the sheer complexity of such a system
implies a high probability of misconfigurations
endangering the overall security. While the benefits of
cloud computing are clear and end-users demand such
services, security is a major inhibitor of cloud
computing adoption on all levels of abstraction. In
numerous studies the security related problems have
been pointed out. One of the top risks exposed in the
study is the failure of isolation in the cloud computing
environment [12].
Cloud computing environments are becoming
increasingly complex, more tenants are sharing the
same physical resources, and the flexibility and
possibility of programmatic configurations can lead to
unforeseen misconfigurations. For example, network-
based storage volumes can be flexibly attached to
virtual machines, and potentially a volume will be
attached to a wrong virtual machine risking the
exposure of sensitive data on t hat volume. Network
security is also flexibly managed through a
programmatic interface, which could lead to problems
resulting in network services exposed wrongly to the
public and opening not properly secured services to
other peers [12]. Administrators of such virtual
infrastructures must be able to easily understand the
complex deployments and ensure that proper security
is given. The dynamic and agility of such
environments also provides a challenge in ensuring the
security over its entire lifetime due to their constant
changes [12].
In order to successfully address the problem of
configuration complexity and potential
misconfigurations in cloud computing environments,
we narrowed down the problem domain to a specific
case of multi-tier applications deployed in
infrastructure clouds using a specific cloud provider as
an example case. We will study existing literature in
the broad domain of virtual machine security, which
plays a f undamental part in the security of
infrastructure clouds, and network security analysis
with a focus on vulnerability assessment and reach-
ability [12]. B ased on the insights and inspirations
obtained by performing the literature review, we will
propose a novel approach in assessing the security of a
multi-tier application deployed on the Amazon
infrastructure cloud. By implementing our approach
and then evaluating it regarding practicality and
scalability, we will determine the practical usefulness
for detecting misconfigurations even in large-scale
deployments. The evaluation is performed both
theoretical and practical. The theoretical evaluation is
conducted by assuming complex configuration
scenarios and analyzes the algorithm run-time using an
ideal computer. The practical evaluation is performed
using the implementation on a sample multi-tier
application deployed on Amazon EC2 [12].
The main contribution of this paper is a novel approach
in the security evaluation of multi-tier virtual
infrastructures, inspired by vulnerability assessment
approaches for traditional computing environments and
applied for the case of the Amazon infrastructure
cloud. The security evaluation consists of an automated
security audit process of the currently deployed
configuration with regard to a given policy specifying
the desired state of the configuration, and an abstract
framework for evaluating the security impact of
configuration changes. Besides the main contribution
stated above, multiple minor contributions can be
pointed out [12]. A comprehensive description of the
underlying architecture of the Amazon infrastructure
cloud is presented, which was publicly only available
in incomplete and fragmented form. We provide a
comparison of two methods for deploying multi-tier
virtual infrastructures on Amazon with regard to the
provided isolation levels [12]. Finally, a data model for
representing the configuration of Amazon deployments
is presented and integrated into a larger data model
capable of representing configurations of different
virtualization systems [12].
Cloud computing is a broad term combining several
different types of service offerings. In general we
distinguish between Software, Platform, and
Infrastructure as a se rvice, which are offered by the
cloud provider [12]. The main focus of this paper lies
on Infrastructure as a Service, also called
Infrastructure Clouds, but for comparison reasons the
other types of offerings are also briefly presented [12].
Storage can be provided in different ways varying
among the multiple IaaS providers. Four different
forms can be identified in the currently available
providers: NAS-like, SAN-like, API-based data
objects, and Virtual Machine storage. A virtual
machine has typically a f ixed-size data storage
available, which is equivalent to a hard disk in a
regular desktop or server computer. In some cases this
type of storage is only intended to be used for
temporary data and is itself non-persistent, i.e., after
the machine terminates the data is lost [12]. NAS-like
storage, like GoGrid Cloud Storage, is accessible from
the VMs on a file-based level using standard protocols
like CIFS. Amazon Elastic Block Store (EBS) is a
SAN-like storage type, which appears to the VM as an
additional block-device. An EBS volume can be
attached to different VMs, but not to multiple VMs
simultaneously, and the size can be adjusted presuming
the file system on the block-device is resizable as well.
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DOI: 10.37394/23204.2022.21.1