City, University of London Institutional Repository
Citation: Modi, C., Patel, D., Borisaniya, B., Patel, A. and Rajarajan, M. (2013). A survey
on security issues and solutions at different layers of Cloud computing. The Journal of
Supercomputing, 63(2), pp. 561-592. doi: 10.1007/s11227-012-0831-5
This is the accepted version of the paper.
This version of the publication may differ from the final published
version.
Permanent repository link: https://openaccess.city.ac.uk/id/eprint/12199/
Link to published version: http://dx.doi.org/10.1007/s11227-012-0831-5
Copyright: City Research Online aims to make research outputs of City,
University of London available to a wider audience. Copyright and Moral
Rights remain with the author(s) and/or copyright holders. URLs from
City Research Online may be freely distributed and linked to.
Reuse: Copies of full items can be used for personal research or study,
educational, or not-for-profit purposes without prior permission or
charge. Provided that the authors, title and full bibliographic details are
credited, a hyperlink and/or URL is given for the original metadata page
and the content is not changed in any way.
City Research Online: http://openaccess.city.ac.uk/ publications@city.ac.uk
City Research Online
1
A Survey on Security Issues and Solutions at Different Layers of
Cloud Computing
Chirag Modi
1
, Dhiren Patel
1
, Bhavesh Borisaniya
1
,
Avi Patel
2
,
Muttukrishnan Rajarajan
2
21
NIT Surat, India
2
City University London, UK
Abstract
Cloud computing offers scalable on-demand services toconsumers with greater flexibility and lesser infrastructure investment.
Since Cloud services are delivered using classical network protocols and formats over the Internet, implicit vulnerabilities
existent in these protocols as well as threats introduced by newer architectures raise many securityand privacy concerns. In
this paper, we survey factors affecting Cloud computing adoption, vulnerabilities,and attacks, and identify relevant solution
directives to strengthen security and privacyin Cloud environment.
Keywords: Cloud Computing; Virtualization; Security; Privacy; Vulnerabilities
1. Introduction
Cloud computing has emerged as a way for IT businesses to increase capabilities on the fly without investing
much in new infrastructure, training of personals or licensing new software [1]. NIST defines Cloud computing
as a "model for enabling ubiquitous, convenient, on demand network access to a shared pool of configurable
computing resources that can be rapidly provisioned and delivered with minimal managerial effort or service
provider interaction” [2]. It follows a simple “pay as you go” model, which allows an organization to pay for only
the service they use. It eliminates the need to maintain an in-house data center by migrating enterprise data to a
remote location at the Cloud provider’s site. Minimal investment, cost reduction and rapid deployment are main
factors that drive industries to utilize Cloud servicesand allow them to focus on core business concerns and
priorities rather than dealing with technical issues. According to [3], 91% of the organizations in US and Europe
agreed that reduction in cost is a major reason for them to migrate to Cloud environment.
2
As shown in Fig. 1, Cloud services are offered in terms of Infrastructure (IaaS), Platform (PaaS) and Software
(SaaS). It follows a bottom up approach wherein at the infrastructure level; machine power is delivered in terms
of CPU consumption to memory allocation. On top of it, lies the layer that delivers an environment in terms of
framework for application development, termed as PaaS. At the top level resides the application layer, delivering
software outsourced through the Internet, eliminating the need for in-house maintenance of sophisticated
software[4]. At application layer, the end users can utilize software running at a remote site by Application
service providers (ASPs). Here, customers need not to buy and install costly software. They can again pay for
only they use and their concerns for maintenanceare cut off. All the software or applications are kept under the
control of service provider.
Fig. 1.Cloud service stack.
1.1. Need for Security and Privacy in Cloud Computing
Cloud computing is a merger of several known technologies including grid and distributed computing,
utilizing Internet as a service delivery network. Public Cloud environment is extremely complex when compared
to a traditional data center environment [2]. Under the paradigm of Cloud computing, an organization surrenders
3
direct control over major aspects of security, conferring a substantial level of trust onto the Cloudprovider. A
survey regarding use of Cloud services made by IDC says that security is the greatest challenge of the Cloud as
shown in Fig. 2 [5].
Fig. 2.Results of IDC ranking security challenges [5].
Virtual environments areused in Cloud to achieve multi-tenancy. Vulnerabilities in virtual machines [6] pose
direct threat to the privacy and security of the Cloud services. Factors crippling usage of Cloud services are live
migration of data over the Internet, entrusting a provider for data security and privacy, vulnerabilities at
browser’s API, vulnerabilities in network, export regulations for encryption etc.
Shared and distributed resources in Cloud systems make it difficult to develop security model for ensuring the
data security and privacy. Due of transparency issues, no Cloud provider allows its customers to implement
intrusion detection or security monitoring system extending into the management services layer behind
virtualized Cloud instances. Customers may not be aware of detailed security-incidents, vulnerability, or malware
reports. For example, through back channel, attackers may be able to access the content of Cloud instances and
fix a kernel level rootkit [7]. Attacks on “physical level” such as reading out the random access memory of the
virtualized hosts or subverting the virtualization layer [8], are known to the community. Even the host system
providing the data can no longer be fully trusted since Cloud provider owns the physical resources.
Cloud service providers often establish a Service Level Agreement (SLA) to highlight security and privacy of
the related service. To an extent, there is a lack of a standard methodology to design a SLA. The authors in [9]
presented SLA about provided services and the waivers. These waivers do not really help the customers fulfilling
their losses. Cloud providers like Amazon, Google, Salesforce etc. rely on detailed SLAs to guarantee security
and other parameters for customers. E.g., Amazon’s EC2 provides abstraction of virtual hardware to its users,
covering all types of failures including operator node failure and software node failure [10]. In future, SLA based
Google App Engine would likely to manage all causes of failures.
Rest of the paper is organized as follows: Section 2 discusses vulnerabilities, threats and attacks relevant to
Cloud. A survey on security issues at different levels inCloud and their existing solutions are provided in section
3. Section 4discussesresearch directionswith conclusionsand references at the end.
2. Vulnerabilities, Threats and Attacks to Cloud Computing
In Cloud, existing vulnerabilities, threats and associated attacks raises several security concerns.
Vulnerabilities in Cloud can be defined as the loopholes in security architecture of Cloud,which can be exploited
by an adversary via sophisticated techniques to gain access of network and other resources. A threat in Cloud is a
potential (or actual adverse) event, that may be malicious or incidental (such as the failure of a storage device),
compromising Cloud resources [11]. An attack is an action to harm Cloud resources. Exploitation of
vulnerabilities would affect the availability and productivity of Cloud computing.
2.1. Vulnerabilities in Cloud Environment
In this section, we discuss major vulnerabilities specific to Cloud, which pose serious threats to Cloud
computing.
2.1.1. Vulnerabilities in virtualization/ multi tenancy
Virtualization/ multi-tenancy serves as the basis for Cloud computing architecture. There are mainly three
types of virtualization are used: OS level virtualization, application based virtualization, and Hpervisor based
virtualization. In OS level virtualization, multiple guest OSs are running on a hosting OS that has visibility and
4
control on each guest OS. In such type of configuration, attacker can get control on the entire guest OSs by
compromising the host OS. In application based virtualization, virtualization is enabled on the top layer of host
OS. In this type of configuration, each VM has its guest OS and related applications. Application based
virtualization also suffers from same vulnerability as in OS based vulnerabilities. Hypervisor or virtual machine
monitor (VMM) that is just like code embedded to host OS. Such code may contain native errors. This code is
available at boot time of host OS to control of multiple guest OSs. If hypervisor is compromised, then the entire
controlled guest OSs can be compromised. Vulnerabilities in virtualization or hypervisor allows attacker to
perform cross-VM side-channel attacks and DoS attacks. For instance, a malformed code in Microsoft’s Hyper-V
is run by an authenticated user in one of the VM caused a DoS attack [53]. In VMware Workstation, an attacker
cause an error to store some malformed data, which enabled a DoS attack on the host OS.
Cloud providers thrive to maintain maximum level of isolation between Virtual machine (VM) instances
including isolation between inter user processes. By compromising the lower layer hypervisor, attacker can gain
control over installed VMs. BLUEPILL [12], SubVirt [13] and DKSM [14] are attack examples on virtual layer.
Through these attacks, hackers can able to modify the installed hypervisor and gain control over the host.
Another incident is vulnerability found in the memory management of Microsoft virtual pc. This has resulted
into user programs running in guest Operating system getting read/write access to bypass security mechanisms
like Data Execution Prevention (DEP), Safe Structured Error Handling (SafeSEH) and Address Space Layout
Randomization (ASLR)[15]. Input validation error in Xencan be exploited by root user of a guest domain to
execute arbitrary commands in domain 0 (Host domain).
2.1.2. Vulnerabilities in Internet protocol
Vulnerabilities in Internet protocols may prove to be an implicit way of attacking Cloud system, that include
common types of attacks like man-in-the-middle attack, IP spoofing, ARP spoofing, DNS poisoning, RIP attacks
and flooding. ARP poisoning is the one of the known vulnerabilities in Internet protocols. Using this
vulnerability, malicious VM can redirect all the inbound/outbound traffic of a co-located VM to the malicious
VM since ARP does not require Proof-of-Origin. HTTP is a web application protocol that requires session state.
Many techniques are used for session handling. However, they are vulnerable to session-riding and session
hijacking. These vulnerabilities are certainly relevant to Cloud.TCP/IP has some “unfixable flaws” such as
“trusted machine” status of machines that have been in contact with each other, and tacit assumption that routing
tables on routers will not be maliciously altered [16].Such attack scenario becomes critical for public Clouds, as
the general backbone for Cloud provision is the Internet.
2.1.3. Unauthorized access to management interface
In Cloud, users have to manage their subscription including Cloud instance, data upload or data computation
through a management interface e.g. AWS management console [17]. Unauthorized access to such a management
interface may become very critical for a Cloud system. Unlike traditional system, higher number of
administrators and users for a Cloud system increases probability for unauthorized access. Advances in crypto
analysis breaks security provided by cryptographic algorithms, which may turns strong encryption into weak
encryption. Insecure or out dated cryptography vulnerabilities are also relavant to Cloud since it is not thinkable
to use Cloud without using cryptography to protect data security and privacy in the cloud. For example, a
cryptographic hole discovered in Amazon’sEC2 management interface by performing signature-wrapping and
cross site scripting (XSS) attacks, where interfaces used to manage Cloud resources are hijacked. Such attacks
allow attackers to create, modify and delete machine images, and change administrative passwords and
settings[18].Recent research [19]has shown that, successfully attacking a Cloud control interface can allows an
attacker to gain a complete power over an account including all stored data.
![Fig. 8. Securing virtual image repository and access control [37].](/figures/fig-8-securing-virtual-image-repository-and-access-control-jbor9ix2.webp)
