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SaaS Apps May Leak Data Even When Encrypted, Study Says

'Side-channel' leaks could lead to exposure of sensitive information, researchers warn
Applications delivered via the software-as-a-service (SaaS) model could be leaking data, according to a research paper published earlier this week.

The paper (PDF), which was prepared by researchers at Microsoft Research and Indiana University, offers a detailed look at the behavior of SaaS-delivered applications and how their use of networks can cause "side-channel" leaks that might enable attackers to glean even the most sensitive data -- even when the SaaS offerings are encrypted.

"Specifically, we found that surprisingly detailed sensitive information is being leaked out from a number of high-profile, top-of-the-line Web applications in healthcare, taxation, investment, and Web search," the paper says.

The leaks don't happen in every SaaS application, the researchers say, and some are worse than others. But the network-oriented behavior of SaaS applications means that the side-channel flaw could be present even in environments that use strong encryption.

"A Web application is split between the browser and the server, so a subset of its internal state-transitions and data exchanges inevitably go through the network," the paper says. "Despite encryption, some fundamental characteristics of Web applications -- namely low entropy input, stateful communications, and significant traffic distinctions -- make the side-channel leak a realistic and serious privacy problem."

Since the vulnerability varies from app to app, SaaS providers and users will have to study their applications individually, the paper says. "Developers will need to identify the vulnerabilities first, and then specify mitigation policies accordingly," the researchers say. "This effort requires analysis of Web application semantics, information flow, and network traffic patterns."

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