Are cloud services safe to use? What are their security weaknesses? What do enterprises need to know before they sign up?

The European Network and Information Security Agency (ENISA) today is publishing a 124-page report designed to answer these questions for enterprises all around the globe. Nearly a year in the making, it covers the technical, policy, and legal implications of cloud services, and makes recommendations for how to address the risks and maximize the benefits.

The report identifies 35 specific risks associated with cloud services, as well as some potential security benefits.

Loss of governance is one chief category of risks, ENISA says. "In using cloud infrastructures, the client necessarily cedes control to the Cloud Provider (CP) on a number of issues which may affect security. At the same time, [service level agreements] may not offer a commitment to provide such services on the part of the cloud provider, thus leaving a gap in security defences."

Enterprises also run the risk of being "locked in" to a single provider, the report says. "There is currently little...that could guarantee data, application and service portability," ENISA observes. "This can make it difficult for the customer to migrate from one provider to another or migrate data and services back to an in-house IT environment. This introduces a dependency on a particular CP for service provision."

In addition, enterprises also risk losing separation from other enterprises in a multi-tenant service, ENISA says. "Multi-tenancy and shared resources are defining characteristics of cloud computing. This risk category covers the failure of mechanisms separating storage, memory, routing, and even reputation between different tenants (e.g., so-called guest-hopping attacks)." These risks are still smaller than the risks posed by attacks on traditional operating systems, the report says.

Cloud services may also jeopardize an enterprise's compliance with some regulatory environments, the report notes. In some cases, it may be difficult to audit and certify a specific enterprise's security in a cloud environment, where many enterprises share a common infrastructure.

Some cloud services may not be able to fully delete data after carrying it, the report says. "When a request to delete a cloud resource is made, as with most operating systems, this may not result in true wiping of the data," ENISA says. "Adequate or timely data deletion may also be impossible, either because extra copies of data are stored but are not available, or because the disk to be destroyed also stores data from other clients."

Cloud services could expose enterprises to new forms of insider threat, ENISA says. "Cloud architectures necessitate certain roles which are extremely high-risk," the report says. "Examples include CP system administrators and managed security service providers." The customer management interfaces to a service provider may also be vulnerable to attack, ENISA warns.

In all, the report identifies 35 specific risks associated with cloud services, including organizational, technical, and legal risks. But the report also suggests that there may be benefits to cloud services, even on the security level.

"The scale and flexibility of cloud computing gives the providers a security edge," ENISA says. "For example, providers can instantly call on extra defensive resources like filtering and re-routing. They can also roll out new security patches more efficiently and keep more comprehensive evidence for diagnostics."

The full 124-page report is available for free via the the ENISA Website.

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