Crypto boffins uncover rogue task risk on Amazon cloud

AWS drops the SOAP, plugs backdoor quickly though

By John Leyden, 27th October 2011

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Security researchers have unearthed a flaw in Amazon Web Services that created a possible mechanism for hackers to take over control of cloud-based systems and run administrative tasks.

The flaw, which affected Amazon's EC2 cloud and has already been plugged, could have been abused to start and stop virtual machines or create new images in an EC2 virtual environment, for example. The root cause of the security weakness stemmed from poor cryptographic practices.

A team of researchers from Germany's Ruhr University found that an XML signature-based attack can be used to manipulate SOAP messages in such a way that EC4 authentication systems fail to detect that they have been doctored – and thus action them as authentic.

The approach applies a class of security shortcoming, involving the modification of partially signed XML documents, that was first uncovered in 2005 as affecting cloud-based systems, H Security reports.

The attack was possible because application signature verification and XML interpretation were handled separately by Amazon's SOAP interface, a security shortcoming that allows unsigned code to be smuggled through gateways onto management systems via maliciously modified messages. "Attackers can move the signed partial tree and then inject specially crafted elements in the original location," H Security explains.

Eucalyptus, an open source-based framework for creating private cloud installations, was similarly vulnerable, according to the Ruhr team.

In an academic paper, the researchers suggest a fix for these so-called signature-wrapping attacks that involves using a "subset of XPath instead of ID attributes to point to the signed subtree", an approach they reckon is both more efficient and secure.

The researchers said Amazon was also vulnerable to cross-site scripting (XSS) attacks that could have allowed users logged onto its online store to hijack an AWS session, using injected JavaScript code. The researchers demonstrated the vulnerability, only possible because signing into Amazon store automatically creates a concurrent AWS cloud service session automatically, at an ACM workshop on cloud security during a presentation entitled All Your Clouds are Belong to us.

The researchers informed both Amazon and Eucalyptus developers of the security flaws prior to their presentation. Both Amazon and Eucalyptus have reportedly fixed the flaws.

More details on the cloud security aspect of their research can be found in a statement by the Ruhr team (in German) here. ®

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