Enterprise to Cloud Security Assessment

A Method using OSSTMM 3.0 Concepts

Ronivon Costa

and Carlos Serrão

VANTIS, R. Rui Teles Palhinha, 6 - 3ºG, 2740-278, Porto Salvo, Portugal

ISCTE-IUL, Av. das Forças Armadas, 1649-026, Lisboa, Portugal

Keywords: Cloud Security, Security Assessment, OSSTMM 3.

Abstract: Much has been talked about security, and with the wide spread and adoption of Cloud computing, the talk

has followed the buzz and put Cloud Security in the spotlights. Security guides for the Cloud has been

published, but we understand that is still missing a practical assessment methodology that would allow

organizations to quick understand how the security of their assets are impacted when it is farmed out to

Public Clouds. Our contribution to address this problem is a method to isolate the organization’s assets from

the environment it is hosted, and compare metrics from the environment only. This method provides the

important benefit of allowing the organization to determine how security will be impacted without having to

actually migrate its resources.

1 INTRODUCTION

The difficult in evaluating security of complex

systems has been an obstacle in the adoption of

Cloud by large organizations, since the security

properties of such services is dependent of several

factors, most of them out of the customer’s control.

One valid approach for an enterprise to verify how a

Cloud provider would satisfy its own security

requirements can be based on actual tests of that

Cloud, but considering that every company wanting

to adopt services from a specific Cloud provider

would have to run its own tests in the process of

evaluation, we can foresee a huge expenditure in

terms of time and cost during the process just to

verify viability. And this expenditure would increase

even more if the process had to be performed for

different projects in the same enterprise. The US

Government has launched the FedRAMP project in

2012 to overcome this issue, and will allow

participating agencies to jump in into Amazon Cloud

services with its projects without requiring a new

evaluation for every project (Reuters, 2013).

Not every Cloud provider will be willing to

allow prospectors testing its resources against

vulnerabilities, since some types of active tests will

trigger security alarms that will be difficult to

differentiate from legitimate, actual threats. One way

to overcome this difficulty is the Provider itself run

the security assessment and to publish the test results

available to all prospectors. Using methodic process

and well accepted metrics, this assessment can be

instrumental in helping a company in the decision of

migrating resources to a Cloud. On such method that

fulfills this requirement is the Open Source Security

Testing Methodology Manual (OSSTMM) and its

rav concept (Herzog, 2010).

Using the rav, it is possible to make sense of the

actual security of a system related to an optimal

state, which can also be compared to other system.

In other terms, one can verify the security of the

enterprise systems when all resources are hosted in

the internal network, and then compare with the

security of the same enterprise with some of its

resources in a Cloud. Although the systems are

different, the rav will provide a metric that can be

related in these very different situations.

In this paper, we explore this characteristic of the

OSSTMM methodology and propose an even more

direct approach to verify how security is affected

when the Cloud is a variable to take into

consideration.

2 PROBLEM

The decision to adopt the Cloud must consider

571

Costa R. and Serrão C. (2013).

Enterprise to Cloud Security Assessment - A Method using OSSTMM 3.0 Concepts.

In Proceedings of the International Conference on Knowledge Discovery and Information Retrieval and the International Conference on Knowledge

Management and Information Sharing, pages 571-578

DOI: 10.5220/0004666005710578

 SCITEPRESS

several factors besides the financial direct benefits.

Cloud adoption can have different effects in the

global security of an enterprise network, and some

of these changes will happen due to the movement

of assets from one site to another and a

corresponding risk transfer (ENISA, 2009).

The above concept can be generally expressed by

the following metaphor: There are three safes, each

one protecting valuable assets: Gold, Silver and

Bronze. There is not enough space in the owner’s

own property to store all three safes, so the owner

will have to rent space somewhere to store one of

them. The decision about which safe will be stored

in the rented space must be based on:

a) the importance of the safe contents (assets);

b) how well protected the safe is now;

c) how well protected will it be in the new place.

The knowledge of a safe existence and place of

storage is a risk factor, and therefore should be

avoided. For example, if it is brought to a thief

knowledge about the existence of a safe full of

valuable assets made of bronze stored in a given

place, all of the other two safes will also be at risk of

being stolen since it is all stored in the same physical

location. If the safe with bronze assets is stored in a

different location, and someone tries to steal its

contents, the other two safes will not be at risk.

The metaphor presented illustrates three

characteristics of the concept used in this work

which are:

 Risk transfer;

 Improved security by limiting the number of

visible targets;

 Influence of the surrounding environment over

the asset’s security.

The schematics in figure 1 illustrates some possible

attack vectors to four targets in a (simplified view)

of a network (left). If the attacker succeeds using

any of the vectors, the compromised internal target

can be used to attack more important targets in the

same network (in the right diagram).

Strategic

Server 1

(Compromised)

Non-Strategic

Server 1

Enterprise

Network

100% of Atack

of the Surface

Strategic

Server 1

Non-Strategic

Server 1

Strategic

Server 2

Non-Strategic

Server 2

Enterprise

Network

100% of Atack

of the Surface

Strategic

Server 2

Non-Strategic

Server 2

Figure 1: Global attack surface.

Moving some targets to a separate environment

will have two effects, which is the change in the

exposure level of the moving targets, and the change

in the exposure level of the remaining targets. This

change can be for good or for bad, and it will depend

on the targets moved, its importance, and how it

interacts with other enterprise components.

Figure 2: Split attack surface.

Every component in a given scope will

contribute to the overall security property of that

environment (Yildiz et al, 2009), and that is the

reason why every target must be included in a

security assessment. However, the surrounding

environment will have an even stronger influence.

Verifying the security of the surrounding

environment using OSSTMM methodology concepts

will allow the comparison of security in absolute

values for both environments by using a metric

called rav (Herzog, 2010).

3 RELATED WORK

There are several evaluation, risk and assessment

methodologies available, as well as guidance to

improve systems security including the cloud (CSA,

NIST, OWASP and etc.). While a few published

guidelines has targeted the Cloud (CSA, 2009)(US

CIO, 2010), most of them are a general framework

or methodology designed as a checklist or a process

to run networking and systems testing.

The process of evaluating Cloud adoption

involves more variables than the security properties

of the systems and environment. We start from the

point where all administrative and political decisions

has already been dismissed as not blocking for the

cloud adoption, and so comes the time to define

which resources are more appropriate to move. The

technical decisions about what can be moved out can

KDIR2013-InternationalConferenceonKnowledgeDiscoveryandInformationRetrieval

572

be evaluated against security metrics previously

obtained from tests performed on predefined models.

The specifics of the tests will not be covered,

however, some guidelines should be followed to

assure that Cloud specific issues are addressed, such

as what to what to test, the approach, and how to

evaluate the results.

OWASP (2012) has started a new chapter

denominated “Cloud-10 Project” to approach Cloud

security risks. OWASP top ten lists are important

because it helps the enterprises to focus on the most

serious threats to web applications, and the Cloud-10

projects is a work in project (Pre-Alpha) to address

this new paradigm in enterprise computing. OWASP

top ten lists are maintained by a community of users

and experts in every domain, and are ranked by

criteria such as (OWASP, 2012):

 Easily Executable

 Most Damaging

 Incidence Frequency (Known)

The OWASP Cloud-10 project defines the criteria

that can guide the security tests, but an appropriate

testing methodology is required. The Open Source

Security Testing Methodology or OSSTMM has its

focus on operational effectiveness, that is, how it

works (Herzog, 2011). OSSTMM3 is an evolution

from a penetration testing methodology which

evolved to more than a best practices framework by

2005 (Herzog, 2010) and finally into a more

contemporary security assessment methodology that

prioritizes tests (avoiding guesses), concentrates on

the interactions and its required protections, and

balance between security and operations (Herzog,

2011).

OSSTMM has redirected its focus in the earlier

releases from testing physical resources such as

firewalls and routers to verifying operational

security and its related channels, such as Human,

Physical, Wireless, Telecommunications, and Data

Networks (Herzog, 2010) in the latest versions of the

methodology. OSSTMM also introduces its own

measurement metrics called ravs, which provides

graphical representation of system’s states and

system state changes over time, and are suitable to

be used in operational monitoring consoles.

The Cloud Security Alliance (CSA) is a non-

profit organization engaged in providing security

awareness and tools to adopters. CSA has a specific

publication providing guidance to Cloud security,

“Security Guidance for Critical Areas of Focus in

Cloud Computing” (CSA, 2009), which is structured

around thirteen domains covering several aspects of

Cloud security, including Identity and Access

Management. CSA has also started the “Consensus

Assessments Initiative” to provide means of

documenting existing controls for Cloud services,

This initiative is based on a questionnaire available

at CSA web site, which can be downloaded, have the

questions answered and then submitted to the

repository of respondents where it can be consulted

by customers.

Guidance is also provided by the US

Government, and targeted to U.S. Federal Agencies

but publicly available. The “Proposed Security

Assessment and Authorization for U.S. Government

Cloud Computing” has a strong focus on

authorization, defines a baseline of security controls

and a monitoring process, and also proposes a

framework to assess cloud security during vetting of

Cloud Service Providers (U.S CIO, 2010).

4 BACKGROUND CONCEPTS

The Figure 3 presents our base line model.

Everything inside the enterprise can be seen as a

controlled environment, while everything in the

outside is beyond its control (Grobauer et al, 2011)

(Hiroyuki et al, 2011), and therefore, must not be

trusted. That is not to say that an intranet is a safe

place to run business without protection, which it is

not. According to the “2011 Cyber Security Watch

Survey - How Bad Is the Insider Threat?” (CERT

2011) carried out by the Carnegie Mellon University

over a population of 607 companies, 27% of all

security incidents were caused by insiders in 2010,

at the same time that 46% of all respondents affirm

that the internal incidents had caused more damage

than the outside attacks.

In the Figure 4 we have extended some services

from the internal enterprise network to a Public

Cloud, while in Figure 5 it was extended further to

provide employee’s access to the organization’s

resources in the Cloud.

Almost any enterprise application can be

configured to work in a Public Cloud. However, two

important factors must be considered:

 The Cloud is not under the Enterprise’s control -

therefore, it can be considered an uncontrolled

environment (Hiroyuki et al, 2011).

 To work with the applications in the Public

Cloud, it is necessary to cross a potential

insecure channel: the Internet.

EnterprisetoCloudSecurityAssessment-AMethodusingOSSTMM3.0Concepts

573

Internet

Servers Clients

Enterprise Intranet

Figure 3: Base line.

Figure 4: Enterprise to Cloud Use Case 1.

Figure 5: Enterprise to Cloud Use Case 2.

The subtle change in the level of trust in the

surrounding environment is more than enough to

make it unviable to apply an unprotected

authentication protocol for services in a Public

Cloud, so there must be a VPN connecting both

separate environments. The risk of exchanging

private, important data over the internet in the

scenario above is a showstopper for most of the

companies. The communication between the clients

on the company’s Intranet and the server in the

Public Cloud can be intercepted in a number of

ways, including by the man-in-the-middle attack and

the eavesdropping technique, to intercept and decode

authentication information and application data.

Several factors that must be considered to choose

the resources to be migrated to the Cloud and not all

of them are related with security, such as the

following provided by (Krutz and Vines, 2010):

 The criticality level of the application

 The sensitivity of the data

 Functionality over VPNs

 Performance

 Cost to move to another provider

 Bandwidth utilization

Since there is not a specific methodology or

framework to assess Cloud security, we have chosen

a generic, more contemporary methodology,

OSSTMM, as a basis for our security assessment.

The OSSTMM proposes a methodology to verify

and test the Operational Security (OpSec) of systems

(Herzog, 2010).

Assessing Cloud security is not a trivial activity,

For the Cloud, some parts of the OpSec procedures

such as physical security and the internal operational

processes can only be assumed to be compliant with

the enterprise’s policies by means of terms of

contracts and SLAs (Hiroyuki et al, 2011) from the

perspective of the customer. Other technical security

properties can be tested, but the lack of Cloud

specific metrics (Grobauer et al, 2011) implies that

we have to propose a method to quantify security for

these use cases, which we do by using the rav

concept, from the OSSTMM (Herzog, 2010).

A security assessment following the OSSTMM

will result in a numeric value representing the level

of security of the assessed system – the rav. When

there are several targets in the scope for a security

assessment, the values obtained for all individual

targets can be combined to produce a final rav,

representing the actual security for the whole

system. The rav calculation can be simplified as

(Herzog, 2010):

Rav = Controls – (Porosity + Limitations)

Where:

 Porosity: The number of visible holes in the

KDIR2013-InternationalConferenceonKnowledgeDiscoveryandInformationRetrieval

574

scope, which means that only what can be

detected during the tests is accounted for the rav.

 Controls: The controls in place to protect the

targets.

 Limitations: also known as “vulnerabilities”, are

derived from the porosity and the controls. The

higher the porosity, higher will be the

limitations. The less controls found, the higher

will be the limitations.

The porosity can be determined by a set of security

tests in the system, which may be comprised of

several individual components. In a security test,

every component in the system will be a target.

There are several tools available to test systems from

several attack vectors and documented in several

literatures as for example by (Wilhem, 2010) and

(McClure at al, 1999). To assess the models in this

work, we have used the OpenVAS, an open source

security vulnerability scanner software.

The OSSTMM is not a methodology to test

Cloud specifically, but a generic methodology to test

many types of IT and non IT systems. The difficulty

to standardize Cloud security assessment and

evaluations is already subject of concerns in the

professional sector (Grobauer et al, 2011). Several

organizations have been making different

contributions, and using different approaches (NIST

2011)(CSA 2009)(OWASP 2012)( USCIO 2010).

In this paper, this difficulty is recognized, but it

is out of scope to develop a specific Cloud security

assessment framework of methodology to evaluate

the results of our study. Instead, the security

assessment was based on the shortcut proposed in

the OSSTMM methodology, which consist of taking

into consideration only the Porosity and Limitations

found, assigning default controls for discovered

services and accepting an uncertain but perhaps

small error margin (Herzog, 2010).

Using the rav metric proposed in the OSSTMM

will make it possible to find a security value for the

baseline relative to the scope, and later compare with

the values obtained from the assessment of the

Cloud model. This comparison between different

systems is supported by the methodology by using

the concept of “Actual Security”, which gives the

actual security of any system in terms of rav (that

can also be seen as a percentage). Using the rav, we

can compare the security of two different systems

and actually understand from each one, how much it

is prepared for the threats against its attack surface

(Herzog, 2010).

In order to focus on specific Cloud security

issues, it was used the concepts presented by

(Grobauer et al, 2011), who proposes that

vulnerabilities are Cloud specific when it:

 is intrinsic to or prevalent in a core cloud

computing technology,

 has its root cause in one of NIST’s essential

cloud characteristics,

 is caused when cloud innovations make tried-

and-tested security controls difficult or

impossible to implement, or

 is prevalent in established state-of-the-art cloud

offerings.

From the above Cloud specific vulnerabilities, we

defined a testing process to include:

 Assessment of the Cloud Web Management

interface (dashboard);

 Assessment for systems from inside the Cloud;

 Assessment from the system from inside the

Cloud using a separate, hostile Tenant;

 Testing all know targets for open TCP/UDP

ports;

 Testing of all knows targets for known Common

Vulnerabilities and Exposures (cve.mitre.org);

5 THE METHOD

The method proposed in this paper follows the

OSSTMM for assessing security, but the main

contribution from that methodology is the metric

called rav. But instead of using the raw value of the

rav that is obtained from the security assessments,

we propose using a delta obtained from the

comparison with a base line model. Using the actual

values calculated for every model will give a

perception of the security for that specific scenario,

when composed by those specific assets with that

specific configuration. On the other hand, using a

delta will make it possible to have an exact

perception of the difference of security derived from

that environment’s influence. The method used in

this work will result in a percentage value, which

will be the final metric to ultimately take the

conclusions about how security is affected after

migrating services to the Cloud. This percentage can

therefore, be applied by different enterprises, or by

the same enterprises in different projects when

evaluating viability of moving resources to that

Cloud. The metric is valid only for that Cloud, but

different assessments can be performed for other

Cloud infrastructures for comparison.

A security assessment using this methodology

EnterprisetoCloudSecurityAssessment-AMethodusingOSSTMM3.0Concepts

575

should always begin by defining a base line model

that will be used as a reference for later comparison

with other models. For a corporate scenario, the base

line should always be the actual organization private

network.

The steps to apply the methodology are:

1. Identify political and administrative issues. Any

identified blocking issue should stop the process

and no further (operational) tests have to be

done. The resource should not be migrated to the

Cloud;

2. Define a security test guideline that can be

applied to both the enterprise and to the Cloud.

This test must include:

 Scope for the enterprise tests. Must include

an external security test (from the Internet).

The internal test must be also part of the

scope, although it may be defined around

only those components that interact with the

relevant targets.

 Scope for the Cloud tests. Must include an

external security test (from the Internet) and

one test from inside the Cloud from a

separate (hostile) tenant. A test from inside

the tenant itself is optional, and depends on if

the systems in the Cloud will have users other

than the administrators.

 Tools to use, including operating system and

version where the tools will run, testing tools

including version and knowledge base

information;

3. Perform the Cloud security test – or request the

security assessment report from the Cloud

provider; the report must contain metrics

according to the OSSTMM, and provide a final

Actual Security value.

4. Perform the Enterprise security test and generate

a report;

It is recommended to use the rav spreadsheet

calculator: (http://www.isecom.org/research/ravs.

html). In this method, the spreadsheet should be

filled with the values obtained in the security tests,

but the controls should have assigned default values

taken from the field “Total” in the “Porosity”

(visibility + access + trust).

The results can be analyzed in two ways:

a) Compare the Actual Security for the two tests;

b) Calculate the percentage variation for the Actual

Security between the Enterprise security

assessment and the Cloud security assessment.

The method in “a” is perfectly allowed by the

OSSTMM methodology and give non related

metrics (Herzog, 2010) which can be used to have

an overall perception of the security provided by the

system.

The method in “b” provides a better perception

of the “gain” or “loss” when comparing two

systems. This method is our proposed methodology

to evaluate the security impact of migrating

resources to a Cloud when we have a previous

reference. Both methods provide valuable decision

information, but the method in “b” will provide a

better understanding of how much security will

influence future use cases.

6 CASE STUDY

This case study was developed for an MSc thesis,

where the authors have setup labs to apply the

method described in this paper. The base line model

in figure 3 was composed of one Windows Domain

Controller, one internal Windows Web server, one

Windows user workstation, one Linux box

configured as both a default router and VPN for the

entire network, and another Linux box running the

public Internet Web Portal. The Internet Web Portal

provided an internet presence as found in most

enterprises, while the internal Web server is for

private, internal use only by the enterprise’s

employees.

Regarding the physical architecture of the Use

Cases, the Base Line model was fully implemented

in a VirtualBox virtualization environment, while

the Enterprise to Cloud Use Cases were

implemented using also an OpenStack IaaS Cloud.

The Cloud was implemented in a single box, and

made accessible from the Internet to allow the

management of the services as required by a Public

Cloud.

In figure 4 and figure 5, the Internet Web portal

and the private internal Web server has been

migrated from the organization’s internal network to

the Public Cloud.

The security assessment of the case study models

were based in the shortcut proposed in the

OSSTMM methodology, which consist of taking

into consideration only the Porosity and Limitations

found, assigning default controls for discovered

services and accepting an uncertain but perhaps

small error margin (Herzog, 2010). Base on that

principle, the results presented below were obtained

filling the rav calculator spreadsheet with the

porosity and limitations detected by OpenVAS

(tables 1, 2, 3 below). Default values were assigned

to the controls, what makes it possible to compare

KDIR2013-InternationalConferenceonKnowledgeDiscoveryandInformationRetrieval

576

different infrastructures using different controls,

which is the most probable scenario when

comparing an organization’s infrastructure with a

Cloud infrastructure. After running the security

assessment using OpenVAS and transporting the

metrics to the rav calculator, we could compare the

results from the Base Line with results from two

models (Use Case 1 and Use Case 2), and came to a

conclusion that the security is not heavily impacted

in the Cloud use cases, with a loss of 2,4601% in the

Use Case 1 and 2.8272% in the Use Case 2 relative

to the Base line model (table 1).

Table 1: Case study results.

Base Line

Use

Case 1

Use

Case 2

Actual Security

(rav)

77.5333 75,6259 75.3413

Variance N/A -2,4601% -2.8272%

The above results were obtained from the

vulnerability assessment which produced the

following data:

Table 2: Porosity.

Base Line Use Case 1 Use Case 2

Visibility 101 148 159

Access 2 4 5

Trust 3 3 4

Table 3: Limitations.

Base Line Use Case 1 Use Case 2

Vulnerabilities 13 24 24

Weaknesses 28 32 32

Concerns 53 76 86

Exposures 15 328 341

Anomalies 0 0 0

The mapping between the Security Assessment and the inputs to

the rav calculator is as follows:

Item How to get

visibility

Number of servers in the use case +

number of unique open ports for all

servers

Access

Interactions points between the servers

and the outside world

Trust

Interactions that do not require

authentication

The Limitations in the rav calculator were mapped directly from

the OpenVAS Results as seen on the next table.

OSSTMM OpenVAS

Vulnerability High Severity

Weaknesses Medium Severity

Concerns Low Severity

Exposures Log

Anomalies False Positives

Applying the concepts proposed in our method,

the variance obtained can be used as a reference

value when the enterprise will require the evaluation

other migrations of resources to the same Cloud,

thus eliminating the necessity of running further

security assessment to determine viability. This

process can be used repeatedly by the enterprise

which will consequently provide several benefits

such as short project life cycles, cost reduction,

7 CONCLUSIONS AND FUTURE

WORK

Using the method proposed by this paper will make

it possible to have a practical and objective view of

the security provided by a specific Cloud provider.

Using the metrics from a security assessment over

that Cloud, one can estimate how much the security

of its assets will be influenced even before migrating

them to that Cloud. Although there will be

considerable resistance from the Cloud provider to

allow for any customer to perform a security testing,

the barrier can be overcome by standardizing the

tests and defining criteria to allow the Cloud

provider to perform them and making the results

publicly available.

Regarding to the method presented in this paper,

we understand that some gaps must be addressed,

such as the depth of the security assessment. In our

case study, the tests was performed using the

OpenVAS security vulnerability scanner software

(www.openvas.org), which does not verify some

Cloud specific issues such as VM isolation, memory

sharing, storage sharing and reuse, etc. Therefore, a

more in depth assessment should include a set of

tools tests to verify virtualization robustness and

isolation effectiveness.

Another improvement can be done in the

verification of the Security Controls. In our study

case, we have used default controls for all the

interaction points and vulnerabilities as supported by

the OSSTMM methodology. The Cloud providers

can add much more value to their security

assessment reports if they decide to actually verify

and report all the controls implemented, thus

reducing the error margin in the results. These

controls may come from an existing source such as

from the “Consensus Assessments Initiative”

questionnaire (CSA, 2011).

EnterprisetoCloudSecurityAssessment-AMethodusingOSSTMM3.0Concepts

577

REFERENCES

Reuters, 2013, “Amazon wins key cloud security

clearance from government”, available online:

http://www.reuters.com/article/2013/05/21/us-amazon-

cloud-idUSBRE94K06S20130521.

European Network and Information Security Agency

(ENISA), (2009), “Cloud: Benefits, risks and

recommendations for information security”,

http://www.enisa.europa.eu/.

Yildiz, M., Abawajy, J., Ercan, T., Bernoth, A., 2009, “A

Layered Security Approach for Cloud Computing

Infrastructure”, 2009. 10th International Symposium

on Pervasive Systems Algorithms, and Networks, IEEE

978-0-7695-3908-9/09, p.763-767.

Herzog, Pete, 2010, “OSSTMM 3 – The Open Source

Security Testing Methodology Manual –

Contemporary Security Test and Analysis”, Institute

for Security and Open Methodologies (ISECOM),

(Online). Available at: http://www.isecom.org/mirror/

OSSTMM.3.pdf.

Herzog, Pete, 2011, “Analyzing the Biggest Bank Robbery

in History: Lessons in OSSTMM Analysis”, Online

Banking Magazine, 2/2011, (Onine). Available at:

http://hakin9.org/analyzing-the-biggest-bank-robbery-

in-history-lessons-in-osstmm-analysis/.

Cloud Security Alliance, 2009, “Security Guidance for

Critical Areas of Focus in Cloud Computing V2.1”,

(Online). Available at: http://www.cloudsecurityal

liance.org/guidance/csaguide.v2.1.pdf.

Cloud Security Alliance, 2011, “Consensus Assessments

Initiative”, (Online). Available at: https://

cloudsecurityalliance.org/research/cai.

U.S. Chief Information Officer, 2010, “Proposed Security

Assessment and Authorization for U.S. Government

Cloud Computing”, (Online). Available at:

http://educationnewyork.com/files/Proposed-Security-

Assessment-and-Authorization-for-Cloud-

Computing.pdf.

OWASP, 2012, “Cloud Top 10 Security Risks”, (Online).

Available at: https://www.owasp.org/index.php/

Category:OWASP_Cloud_%E2%80%90_10_Project.

Grobauer, B., Walloschek, T., Stöcker, E., 2011.

"Understanding Cloud Computing Vulnerabilities". In

IEEE Security & Privacy, vol. 9, no. 2, pp. 50-57,

March-April 2011, doi:10.1109/MSP.2010.115,

(Online). Available at: http://www.computer.org/csdl/

mags/sp/2011/02/msp2011020050-abs.html.

Hiroyuki, S., Shigeaki, T., Atsushi, K., 2011, “Building a

Security Aware Cloud by Extending Internal Control

to Cloud”, 2011 Tenth International Symposium on

Autonomous Decentralized Systems, IEEE 978-0-

7695-4349-9/11, p. 323-326.

CERT, 2011, “2011 CyberSecurityWatch Survey - How

Bad Is the Insider Threat?”, Carnegie Mellon

University, (Online). Available at: http://www.cert.

org/archive/pdf/CyberSecuritySurvey2011Data.pdf.

Cloud Computing Use Cases Group, 2010, “Cloud

Computing Use Cases Version 4.0” (Online).

Available at: http://cloudusecases.org.

Krutz, R., Vines, R., 2010, Cloud Security: A

Comphrehensive Guide to Secure Cloud Computing,

Wiley Publishing, Indianápolis.

NIST, 2011, “The NIST Definition of Cloud Computing”,

National Institute of Standards and Technology – U.S

Department of Commerce, NIST Special Publication

800-145 (Online). Available at: http://csrc.nist.gov/

publications/nistpubs/800-145/SP800-145.pdf.

Wilhelm, T., 2010, Professional Penetration Testing,

Elsevier Inc, Burlington.

McClure, S., Scambray, J., Kurtz, G., 1999, Hacking

Exposed: Network Security Secrets and Solutions,

Oxborne, California.

KDIR2013-InternationalConferenceonKnowledgeDiscoveryandInformationRetrieval

578