Understanding Cloud Computing Vulnerabilities

This article first appeared in Security & Privacy IEEE magazine and is brought to you by InfoQ & IEEE Computer Society.

Discussions about cloud computing security often fail to distinguish general issues from cloud-specific issues. To clarify the discussions regarding vulnerabilities, the authors define indicators based on sound definitions of risk factors and cloud computing.

Each day, a fresh news item, blog entry, or other publication warns us about cloud computing’s security risks and threats; in most cases, secu­rity is cited as the most substantial roadblock for cloud computing uptake. But this discourse about cloud computing security issues makes it difficult to formulate a well-founded assessment of the actual se­curity impact for two key reasons. First, in many of these discussions about risk, basic vocabulary terms - including risk, threat, and vulnerability - are often used interchangeably, without regard to their respective definitions. Second, not every issue raised is specific to cloud computing.

To achieve a well-founded understanding of the “delta” that cloud computing adds with respect to se­curity issues, we must analyze how cloud computing influences established security issues. A key factor here is security vulnerabilities: cloud computing makes cer­tain well-understood vulnerabilities more significant as well as adds new ones to the mix. Before we take a closer look at cloud-specific vulnerabilities, however, we must first establish what a “vulnerability” really is.

Vulnerability: An Overview

Vulnerability is a prominent factor of risk. ISO 27005 defines risk as “the potential that a given threat will exploit vulnerabilities of an asset or group of assets and thereby cause harm to the organization,” measuring it in terms of both the likelihood of an event and its con­sequence[1]. The Open Group’s risk taxonomy of­fers a useful overview of risk factors (see Figure 1).

(Click on the image to enlarge it.)

Figure 1. Factors contributing to risk according to the Open Group’s risk taxonomy. Risk corresponds to the product of loss event frequency (left) and probable loss magnitude (right). Vulnerabilities influence the loss event frequency.

 The Open Group’s taxono­my uses the same two top-level risk factors as ISO 27005: the likelihood of a harm­ful event (here, loss event frequency) and its consequence (here, probable loss magnitude).1 The probable loss mag­nitude’s subfactors (on the right in Figure 1) influence a harmful event’s ultimate cost. The loss event frequen­cy subfactors (on the left) are a bit more complicated. A loss event occurs when a threat agent (such as a hacker) successfully exploits a vulnerability. The frequency with which this happens depends on two factors:

• The frequency with which threat agents try to ex­ploit a vulnerability. This frequency is determined by both the agents’ motivation (What can they gain with an attack? How much effort does it take? What is the risk for the attackers?) and how much access (“contact”) the agents have to the attack targets.
• The difference between the threat agents’ attack ca­pabilities and the system’s strength to resist the attack.

This second factor brings us toward a useful defini­tion of vulnerability.

Defining Vulnerability

According to the Open Group’s risk taxonomy,

“Vulnerability is the probability that an asset will be unable to resist the actions of a threat agent. Vulner­ability exists when there is a difference between the force being applied by the threat agent, and an ob­ject’s ability to resist that force.”

So, vulnerability must always be described in terms of resistance to a certain type of attack. To provide a real-world example, a car’s inability to protect its driver against injury when hit frontally by a truck driving 60 mph is a vulnerability; the resistance of the car’s crumple zone is simply too weak compared to the truck’s force. Against the “attack” of a biker, or even a small car driving at a more moderate speed, the car’s resistance strength is perfectly adequate.

We can also describe computer vulnerability - that is, security-related bugs that you close with vendor-provided patches - as a weakening or removal of a certain resistance strength. A buffer-overflow vulnerability, for example, weakens the system’s resistance to arbitrary code execution. Whether attackers can exploit this vulnerability depends on their capabilities.

Vulnerabilities and Cloud Risk

We’ll now examine how cloud computing influences the risk factors in Figure 1, starting with the right-hand side of the risk factor tree.

From a cloud customer perspective, the right-hand side dealing with probable magnitude of future loss isn’t changed at all by cloud computing: the con­sequences and ultimate cost of, say, a confidentiality breach, is exactly the same regardless of whether the data breach occurred within a cloud or a conven­tional IT infrastructure. For a cloud service provider, things look somewhat different: because cloud com­puting systems were previously separated on the same infrastructure, a loss event could entail a consider­ably larger impact. But this fact is easily grasped and incorporated into a risk assessment: no conceptual work for adapting impact analysis to cloud comput­ing seems necessary.

So, we must search for changes on Figure 1’s left-hand side - the loss event frequency. Cloud comput­ing could change the probability of a harmful event’s occurrence. As we show later, cloud computing causes significant changes in the vulnerability factor. Of course, moving to a cloud infrastructure might change the attackers’ access level and motivation, as well as the effort and risk - a fact that must be considered as future work. But, for supporting a cloud-specific risk assess­ment, it seems most profitable to start by examining the exact nature of cloud-specific vulnerabilities.

Cloud Computing

Is there such a thing as a “cloud-specific” vulnerabil­ity? If so, certain factors in cloud computing’s nature must make a vulnerability cloud-specific.

Essentially, cloud computing combines known technologies (such as virtualization) in ingenious ways to provide IT services “from the conveyor belt” us­ing economies of scale. We’ll now look closer at what the core technologies are and which characteristics of their use in cloud computing are essential.

Core Cloud Computing Technologies

Cloud computing builds heavily on capabilities avail­able through several core technologies:

• Web applications and services. Software as a service (SaaS) and platform as a service (PaaS) are unthink­able without Web application and Web services technologies: SaaS offerings are typically imple­mented as Web applications, while PaaS offerings provide development and runtime environments for Web applications and services. For infrastructure as a service (IaaS) offerings, administrators typically implement associated services and APIs, such as the management access for customers, using Web application/service technologies.
• Virtualization IaaS offerings. These technologies have virtualization techniques at their very heart; because PaaS and SaaS services are usually built on top of a supporting IaaS infrastructure, the importance of virtualization also extends to these service models. In the future, we expect virtualization to develop from virtualized servers toward computational resources that can be used more readily for executing SaaS services.
• Cryptography. Many cloud computing security re­quirements are solvable only by using cryptographic techniques.

As cloud computing develops, the list of core tech­nologies is likely to expand.

Essential Characteristics

In its description of essential cloud characteristics[2], the US National Institute of Standards and Technology (NIST) captures well what it means to provide IT ser­vices from the conveyor belt using economies of scale:

• On-demand self-service. Users can order and manage services without human interaction with the ser­vice provider, using, for example, a Web portal and management interface. Provisioning and de-provi­sioning of services and associated resources occur automatically at the provider.
• Ubiquitous network access. Cloud services are accessed via the network (usually the Internet), using stan­dard mechanisms and protocols.
• Resource pooling. Computing resources used to pro­vide the cloud service are realized using a homo­geneous infrastructure that’s shared between all service users.
• Rapid elasticity. Resources can be scaled up and down rapidly and elastically.
• Measured service. Resource/service usage is constantly metered, supporting optimization of resource usage, usage reporting to the customer, and pay-as-you-go business models.

NIST’s definition framework for cloud computing with its list of essential characteristics has by now evolved into the de facto standard for defining cloud computing.

Cloud-Specific Vulnerabilities

Based on the abstract view of cloud computing we presented earlier, we can now move toward a defini­tion of what constitutes a cloud-specific vulnerability. A vulnerability is cloud specific if 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.

We now examine each of these four indicators.

Core-Technology Vulnerabilities

Cloud computing’s core technologies - Web applica­tions and services, virtualization, and cryptography - have vulnerabilities that are either intrinsic to the technology or prevalent in the technology’s state-of-the-art implementations. Three examples of such vul­nerabilities are virtual machine escape, session riding and hijacking, and insecure or obsolete cryptography.

First, the possibility that an attacker might success­fully escape from a virtualized environment lies in virtualization’s very nature. Hence, we must consider this vulnerability as intrinsic to virtualization and highly relevant to cloud computing.

Second, Web application technologies must over­come the problem that, by design, the HTTP proto­col is a stateless protocol, whereas Web applications require some notion of session state. Many techniques implement session handling and - as any security pro­fessional knowledgeable in Web application security will testify - many session handling implementations are vulnerable to session riding and session hijack­ing. Whether session riding/hijacking vulnerabilities are intrinsic to Web application technologies or are “only” prevalent in many current implementations is arguable; in any case, such vulnerabilities are certainly relevant for cloud computing.

Finally, cryptanalysis advances can render any cryptographic mechanism or algorithm insecure as novel methods of breaking them are discovered. It’s even more common to find crucial flaws in crypto­graphic algorithm implementations, which can turn strong encryption into weak encryption (or sometimes no encryption at all). Because broad uptake of cloud computing is unthinkable without the use of cryptog­raphy to protect data confidentiality and integrity in the cloud, insecure or obsolete cryptography vulner­abilities are highly relevant for cloud computing.

Essential Cloud Characteristic Vulnerabilities

As we noted earlier, NIST describes five essential cloud characteristics: on-demand self-service, ubiqui­tous network access, resource pooling, rapid elasticity, and measured service.

Following are examples of vulnerabilities with root causes in one or more of these characteristics:

• Unauthorized access to management interface. The cloud characteristic on-demand self-service requires a management interface that’s accessible to cloud ser­vice users. Unauthorized access to the management interface is therefore an especially relevant vulnerability for cloud systems: the probability that unau­thorized access could occur is much higher than for traditional systems where the management func­tionality is accessible only to a few administrators.
• Internet protocol vulnerabilities. The cloud characteristic ubiquitous network access means that cloud services are accessed via network using standard protocols. In most cases, this network is the Internet, which must be considered untrusted. Internet protocol vulnerabilities - such as vulnerabilities that allow man-in-the-middle attacks - are therefore relevant for cloud computing.
• Data recovery vulnerability. The cloud characteristics of pooling and elasticity entail that resources allocated to one user will be reallocated to a different user at a later time. For memory or storage resources, it might therefore be possible to recover data written by a previous user.
• Metering and billing evasion. The cloud characteristic of measured service means that any cloud service has a metering capability at an abstraction level ap­propriate to the service type (such as storage, pro­cessing, and active user accounts). Metering data is used to optimize service delivery as well as billing. Relevant vulnerabilities include metering and bill­ing data manipulation and billing evasion.

Thus, we can leverage NIST’s well-founded defi­nition of cloud computing in reasoning about cloud computing issues.

Defects in Known Security Controls

Vulnerabilities in standard security controls must be considered cloud specific if cloud innovations directly cause the difficulties in implementing the controls. Such vulnerabilities are also known as control challenges.

Here, we treat three examples of such control chal­lenges. First, virtualized networks offer insufficient net­work-based controls. Given the nature of cloud services, the administrative access to IaaS network infrastructure and the ability to tailor network infrastructure are typically limited; hence, standard controls such as IP-based network zoning can’t be applied. Also, standard tech­niques such as network-based vulnerability scanning are usually forbidden by IaaS providers because, for example, friendly scans can’t be distinguished from at­tacker activity. Finally, technologies such as virtualiza­tion mean that network traffic occurs on both real and virtual networks, such as when two virtual machine en­vironments (VMEs) hosted on the same server commu­nicate. Such issues constitute a control challenge because tried and tested network-level security controls might not work in a given cloud environment.

The second challenge is in poor key management procedures. As noted in a recent European Network and Information Security Agency study[3], cloud com­puting infrastructures require management and stor­age of many different kinds of keys. Because virtual machines don’t have a fixed hardware infrastructure and cloud-based content is often geographically dis­tributed, it’s more difficult to apply standard con­trols - such as hardware security module (HSM) storage - to keys on cloud infrastructures.

Finally, security metrics aren’t adapted to cloud infrastructures. Currently, there are no standardized cloud-specific security metrics that cloud customers can use to monitor the security status of their cloud resources. Until such standard security metrics are de­veloped and implemented, controls for security assess­ment, audit, and accountability are more difficult and costly, and might even be impossible to employ.

Prevalent Vulnerabilities in State-of-the-Art Cloud Offerings

Although cloud computing is relatively young, there are already myriad cloud offerings on the market. Hence, we can complement the three cloud-specific vulnerabil­ity indicators presented earlier with a forth, empirical indicator: if a vulnerability is prevalent in state-of-the-art cloud offerings, it must be regarded as cloud-specific. Examples of such vulnerabilities include injection vul­nerabilities and weak authentication schemes.

Injection vulnerabilities are exploited by manipu­lating service or application inputs to interpret and execute parts of them against the programmer’s in­tentions. Examples of injection vulnerabilities include

• SQL injection, in which the input contains SQL code that’s erroneously executed in the database back end;
• command injection, in which the input contains commands that are erroneously executed via the OS; and
• cross-site scripting, in which the input contains JavaScript code that’s erroneously executed by a vic­tim’s browser.

In addition, many widely used authentication mechanisms are weak. For example, usernames and passwords for authentication are weak due to

• insecure user behavior (choosing weak passwords, reusing passwords, and so on), and
• inherent limitations of one-factor authentication mechanisms.

Also, the authentication mechanisms’ implementa­tion might have weaknesses and allow, for example, credential interception and replay. The majority of Web applications in current state-of-the-art cloud services employ usernames and passwords as authenti­cation mechanism.

Architectural Components and Vulnerabilities

Cloud service models are commonly divided into SaaS, PaaS, and IaaS, and each model influences the vulner­abilities exhibited by a given cloud infrastructure. It’s helpful to add more structure to the service model stacks: Figure 2 shows a cloud reference architecture that makes the most important security-relevant cloud components explicit and provides an abstract overview of cloud computing for security issue analysis.

Figure 2. The cloud reference architecture. We map cloud-specific vulnerabilities to components of this reference architecture, which gives us an overview of which vulnerabilities might be relevant for a given cloud service.

The reference architecture is based on work carried out at the University of California, Los Angeles, and IBM[4]. It inherits the layered approach in that layers can encompass one or more service components. Here, we use “service” in the broad sense of providing something that might be both material (such as shelter, power, and hardware) and immaterial (such as a runtime environ­ment). For two layers, the cloud software environment and the cloud software infrastructure, the model makes the layers’ three main service components - computa­tion, storage, and communication - explicit. Top lay­er services also can be implemented on layers further down the stack, in effect skipping intermediate layers. For example, a cloud Web application can be imple­mented and operated in the traditional way - that is, running on top of a standard OS without using dedi­cated cloud software infrastructure and environment components. Layering and compositionality imply that the transition from providing some service or function in-house to sourcing the service or function can take place between any of the model’s layers.

In addition to the original model, we’ve identified supporting functions relevant to services in several layers and added them to the model as vertical spans over several horizontal layers.

Our cloud reference architecture has three main parts:

• Supporting (IT) infrastructure. These are facilities and services common to any IT service, cloud or other­wise. We include them in the architecture because we want to provide the complete picture; a full treatment of IT security must account for a cloud service’s non-cloud-specific components.
• Cloud-specific infrastructure. These components con­stitute the heart of a cloud service; cloud-specific vulnerabilities and corresponding controls are typi­cally mapped to these components.
• Cloud service consumer. Again, we include the cloud service customer in the reference architecture because it’s relevant to an all-encompassing security treatment.

Also, we make explicit the network that separates the cloud service consumer from the cloud infrastructure; the fact that access to cloud resources is carried out via a (usually untrusted) network is one of cloud comput­ing’s main characteristics.

Using the cloud reference architecture’s structure, we can now run through the architecture’s compo­nents and give examples of each component’s cloud-specific vulnerabilities. 

Cloud Software Infrastructure and Environment

The cloud software infrastructure layer provides an abstrac­tion level for basic IT resources that are offered as ser­vices to higher layers: computational resources (usually VMEs), storage, and (network) communication. These services can be used individually, as is typically the case with storage services, but they’re often bundled such that servers are delivered with certain network con­nectivity and (often) access to storage. This bundle, with or without storage, is usually referred to as IaaS.

The cloud software environment layer provides servic­es at the application platform level:

• a development and runtime environment for servic­es and applications written in one or more supported languages;
• storage services (a database interface rather than file share); and
• communication infrastructure, such as Microsoft’s Azure service bus.

Vulnerabilities in both the infrastructure and envi­ronment layers are usually specific to one of the three resource types provided by these two layers. However, cross-tenant access vulnerabilities are relevant for all three resource types. The virtual machine escape vul­nerability we described earlier is a prime example. We used it to demonstrate a vulnerability that’s intrinsic to the core virtualization technology, but it can also be seen as having its root cause in the essential char­acteristic of resource pooling: whenever resources are pooled, unauthorized access across resources becomes an issue. Hence, for PaaS, where the technology to separate different tenants (and tenant services) isn’t necessarily based on virtualization (although that will be increasingly true), cross-tenant access vulnerabili­ties play an important role as well. Similarly, cloud storage is prone to cross-tenant storage access, and cloud communication - in the form of virtual net­working - is prone to cross-tenant network access. 

Computational Resources

A highly relevant set of computational resource vulner­abilities concerns how virtual machine images are han­dled: the only feasible way of providing nearly identical server images - thus providing on-demand service for virtual servers - is by cloning template images.

Vulnerable virtual machine template images cause OS or application vulnerabilities to spread over many systems. An attacker might be able to analyze config­uration, patch level, and code in detail using admin­istrative rights by renting a virtual server as a service customer and thereby gaining knowledge helpful in attacking other customers’ images. A related problem is that an image can be taken from an untrustworthy source, a new phenomenon brought on especially by the emerging marketplace of virtual images for IaaS services. In this case, an image might, for example, have been manipulated so as to provide back-door ac­cess for an attacker.

Data leakage by virtual machine replication is a vulnerability that’s also rooted in the use of cloning for providing on-demand service. Cloning leads to data leakage problems regarding machine secrets: cer­tain elements of an OS - such as host keys and crypto­graphic salt values - are meant to be private to a single host. Cloning can violate this privacy assumption. Again, the emerging marketplace for virtual machine images, as in Amazon EC2, leads to a related problem: users can provide template images for other users by turning a running image into a template. Depending on how the image was used before creating a template from it, it could contain data that the user doesn’t wish to make public.

There are also control challenges here, including those related to cryptography use. Cryptographic vul­nerabilities due to weak random number generation might exist if the abstraction layer between the hard­ware and OS kernel introduced by virtualization is problematic for generating random numbers within a VME. Such generation requires an entropy source on the hardware level. Virtualization might have flawed mechanisms for tapping that entropy source, or hav­ing several VMEs on the same host might exhaust the available entropy, leading to weak random number generation. As we noted earlier, this abstraction layer also complicates the use of advanced security controls, such as hardware security modules, possibly leading to poor key management procedures. 

Storage

In addition to data recovery vulnerability due to re­source pooling and elasticity, there’s a related control challenge in media sanitization, which is often hard or impossible to implement in a cloud context. For exam­ple, data destruction policies applicable at the end of a life cycle that require physical disk destruction can’t be carried out if a disk is still being used by another tenant.

Because cryptography is frequently used to overcome storage-related vulnerabilities, this core technology’s vulnerabilities - insecure or obsolete cryptography and poor key management - play a spe­cial role for cloud storage. 

Communication

The most prominent example of a cloud communi­cations service is the networking provided for VMEs in an IaaS environment. Because of resource pool­ing, several customers are likely to share certain net­work infrastructure components: vulnerabilities of shared network infrastructure components, such as vulnerabilities in a DNS server, Dynamic Host Con­figuration Protocol, and IP protocol vulnerabilities, might enable network-based cross-tenant attacks in an IaaS infrastructure.

Virtualized networking also presents a control challenge: again, in cloud services, the administrative access to IaaS network infrastructure and the possi­bility for tailoring network infrastructure are usually limited. Also, using technologies such as virtualiza­tion leads to a situation where network traffic occurs not only on “real” networks but also within virtual­ized networks (such as for communication between two VMEs hosted on the same server); most imple­mentations of virtual networking offer limited possi­bilities for integrating network-based security. All in all, this constitutes a control challenge of insufficient network-based controls because tried-and-tested network-level security controls might not work in a given cloud environment. 

Cloud Web Applications

A Web application uses browser technology as the front end for user interaction. With the increased up­take of browser-based computing technologies such as JavaScript, Java, Flash, and Silverlight, a Web cloud application falls into two parts:

• an application component operated somewhere in the cloud, and
• a browser component running within the user’s browser.

In the future, developers will increasingly use tech­nologies such as Google Gears to permit offline us­age of a Web application’s browser component for use cases that don’t require constant access to remote data. We’ve already described two typical vulnerabilities for Web application technologies: session riding and hijacking vulnerabilities and injection vulnerabilities.

Other Web-application-specific vulnerabilities concern the browser’s front-end component. Among them are client-side data manipulation vulnerabilities, in which users attack Web applications by manipulat­ing data sent from their application component to the server’s application component. In other words, the input received by the server component isn’t the “ex­pected” input sent by the client-side component, but altered or completely user-generated input. Further­more, Web applications also rely on browser mecha­nisms for isolating third-party content embedded in the application (such as advertisements, mashup com­ponents, and so on). Browser isolation vulnerabilities might thus allow third-party content to manipulate the Web application. 

Services and APIs

It might seem obvious that all layers of the cloud in­frastructure offer services, but for examining cloud infrastructure security, it’s worthwhile to explicitly think about all of the infrastructure’s service and ap­plication programming interfaces. Most services are likely Web services, which share many vulnerabilities with Web applications. Indeed, the Web application layer might be realized completely by one or more Web services such that the application URL would only give the user a browser component. Thus the supporting services and API functions share many vulnerabilities with the Web applications layer. 

Management Access

NIST’s definition of cloud computing states that one of cloud services’ central characteristics is that they can be rapidly provisioned and released with minimal man­agement effort or service provider interaction. Con­sequently, a common element of each cloud service is a management interface - which leads directly to the vulnerability concerning unauthorized access to the management interface. Furthermore, because man­agement access is often realized using a Web applica­tion or service, it often shares the vulnerabilities of the Web application layer and services/API component. 

Identity, Authentication, Authorization, and Auditing Mechanisms

All cloud services (and each cloud service’s management interface) require mechanisms for identity management, authentication, authorization, and auditing (IAAA). To a certain extent, parts of these mechanisms might be factored out as a stand-alone IAAA service to be used by other services. Two IAAA elements that must be part of each service implementation are execution of adequate authorization checks (which, of course, use authentica­tion and/or authorization information received from an IAA service) and cloud infrastructure auditing.

Most vulnerabilities associated with the IAAA component must be regarded as cloud-specific be­cause they’re prevalent in state-of-the-art cloud of­ferings. Earlier, we gave the example of weak user authentication mechanisms; other examples include

• Denial of service by account lockout. One often-used security control - especially for authentication with username and password - is to lock out accounts that have received several unsuccessful authentica­tion attempts in quick succession. Attackers can use such attempts to launch DoS attacks against a user.
• Weak credential-reset mechanisms. When cloud com­puting providers manage user credentials themselves rather than using federated authentication, they must provide a mechanism for resetting credentials in the case of forgotten or lost credentials. In the past, password-recovery mechanisms have proven particularly weak.
• Insufficient or faulty authorization checks. State-of-the-art Web application and service cloud offerings are often vulnerable to insufficient or faulty authoriza­tion checks that can make unauthorized information or actions available to users. Missing authorization checks, for example, are the root cause of URL-guessing attacks. In such attacks, users modify URLs to display information of other user accounts.
• Coarse authorization control. Cloud services’ manage­ment interfaces are particularly prone to offering authorization control models that are too coarse. Thus, standard security measures, such as duty sepa­ration, can’t be implemented because it’s impossible to provide users with only those privileges they strictly require to carry out their work.
• Insufficient logging and monitoring possibilities. Current­ly, no standards or mechanisms exist to give cloud customers logging and monitoring facilities within cloud resources. This gives rise to an acute prob­lem: log files record all tenant events and can’t easily be pruned for a single tenant. Also, the provider’s security monitoring is often hampered by insuffi­cient monitoring capabilities. Until we develop and implement usable logging and monitoring standards and facilities, it’s difficult - if not impossible - to implement security controls that require logging and monitoring.

Of all these IAAA vulnerabilities, in the experi­ence of cloud service providers, currently, authentica­tion issues are the primary vulnerability that puts user data in cloud services at risk[5]. 

Provider

Vulnerabilities that are relevant for all cloud comput­ing components typically concern the provider - or rather users’ inability to control cloud infrastructure as they do their own infrastructure. Among the control challenges are insufficient security audit possibilities, and the fact that certification schemes and security metrics aren’t adopted to cloud computing. Further, standard security controls regarding audit, certifica­tion, and continuous security monitoring can’t be implemented effectively.

Cloud computing is in constant development; as the field matures, additional cloud-specific vulnerabilities certainly will emerge, while others will become less of an issue. Using a precise definition of what constitutes a vulnerability from the Open Group’s risk taxonomy and the four indicators of cloud-specific vulnerabilities we identify here offers a precision and clarity level often lacking in current discourse about cloud computing security.

Control challenges typically highlight situations in which otherwise successful security controls are inef­fective in a cloud setting. Thus, these challenges are of special interest for further cloud computing secu­rity research. Indeed, many current efforts - such as the development of security metrics and certification schemes, and the move toward full-featured virtual­ized network components - directly address control challenges by enabling the use of such tried-and-tested controls for cloud computing.

About the Authors

Bernd Grobauer is a senior consultant in information security and leads the Siemens Computer Emergency Response Team’s (CERT’s) research activities in incident detection and han­dling, malware defense, and cloud computing security. Gro­bauer has a PhD in computer science from Aarhus University, Denmark. He’s on the membership advisory committee of the International Information Integrity Institute. Contact him at bernd.grobauer@siemens.com.

Tobias Walloschek is a senior management consultant at Sie­mens IT Solutions and Services GmbH. His research interests are cloud computing security and business adoption strate­gies. Walloschek has a bachelor’s degree in business admin­istration from the University of Applied Sciences in Ingolstadt, Germany. He is a Certified Information Systems Security Pro­fessional. Contact him at tobias.walloschek@siemens.com.

Elmar Stöcker is a manager at Siemens IT Solutions and Ser­vices GmbH, where he’s responsible for the portfolio strat­egy and governance of the professional services portfolio; he also leads the cloud computing security and PaaS activi­ties. Stöcker has a master’s degree in computer science from RWTH Aachen, Germany. Contact him at elmar.stoecker@siemens.com.

IEEE Security & Privacy's primary objective is to stimulate and track advances in security, privacy, and dependability and present these advances in a form that can be useful to a broad cross-section of the professional community -- ranging from academic researchers to industry practitioners.

[1] ISO/IEC 27005:2007 Information Technology—Security Techniques—Information Security Risk Management, Int’l Org. Standardization, 2007.

[2] P. Mell and T. Grance, “Effectively and Securely Using the Cloud Computing Paradigm (v0.25),” presentation, US Nat’l Inst. Standards and Technology, 2009; 

[3] European Network and Information Security Agency (ENISA), Cloud Computing: Benefits, Risks and Recom­mendations for Information Security, Nov. 2009; 

[4] L. Youseff, M. Butrico, and D. Da Silva, “Towards a Unified Ontology of Cloud Computing,” Proc. Grid Computing Environments Workshop (GCE), IEEE Press, 2008; doi: 10.1109/GCE.2008.4738443.

[5] E. Grosse, “Security at Scale,” invited talk, ACM Cloud Security Workshop (CCSW), 2010;