Significant flaws in the implementation of cloud infrastructure services could be putting clients' data at risk.
Research by Context Security said that a vulnerability around data separation allowed its consultants to gain access to some data that was left on other service users' "dirty disks", including fragments of customer databases and elements of system information.
The vulnerability itself is in the way in which some providers automatically provision new virtual servers, initialise operating systems and allocate new storage space.
For performance reasons or due to errors, security measures to provide separation between different nodes on a multi-user platform sometimes are not implemented, making it possible to read areas of other virtual disks and so gain access to data which exists with the physical storage provider.
Context said that it tested four providers and found that two of them, VPS.NET and Rackspace, were not always securely separating virtual servers or nodes through shared hard disk and network resources.
In line with Context's responsible disclosure procedures, both providers were immediately informed of the findings.
Rackspace worked with Context to identify and fix the potential vulnerability, which was found among some users of its now-legacy platform for Linux Cloud Servers.
Rackspace reports that it knows of no instance in which any customer's data was seen or exploited by an unauthorised party.
Context has tested Rackspace's current cloud platform as well as its new next-generation cloud computing solution based on OpenStack, and confirmed that the security vulnerability has been resolved.
But it warned other providers that they might be vulnerable if they use popular hypervisor software, and implement it in the way that Rackspace did before its remediation efforts.
Rackspace has also undertaken efforts to ensure that any data deleted from its physical disk is 'zeroed' to prevent new servers seeing other users, and has taken measures to clean up all existing virtual disks on what is now its legacy cloud server platform.
VPS.NET told Context that it rolled out a patch to resolve the security issue, but provided no details.
It said that its platform is based on OnApp technology that is also used by more than 250 other cloud providers.
OnApp told Context that it now allows customers to opt-in to having their data removed securely, leaving thousands of virtual machines at potential risk.
It added that it had not taken measures to clean up remnant data left by providers or customers, on the ground that few customers were affected.
"In the cloud, instead of facing an infrastructure based on separate physical boxes, an attacker can purchase a node from the same provider and attempt an attack on the target organisation from the same physical machine and using the same physical resources," Context research and development manager Michael Jordon said.
“This does not mean that the cloud is unsafe, and the business benefits remain compelling, but the simplicity of this issue raises important questions about the maturity of cloud technology and the level of security and testing undertaken in some instances.”