Savage and his co-authors Thomas Ristenpart, Eran Tromer and Hovav Shacham were also able to measure the cache activity when the computer was performing simple tasks such as loading a particular Web page. They believe that this method could be used to do things such as see how many Internet users were visiting a server or even which pages they were viewing.
To make their simple attacks work, the researchers had to not only figure out which EC2 machine was running the program they wanted to attack, they also had to find a way to get their particular program on it. This isn't easily done, because cloud computing is, by definition, supposed to make this kind of information invisible to the user.
But by doing an in-depth analysis of DNS (Domain Name System) traffic and using a network-monitoring tool called traceroute, the researchers were able to work out a technique that could give them a 40 percent chance of placing their attack code on the same server as their victim. The cost of the attack on EC2 was just a few dollars, Savage said.
Virtual machines may do a good job of isolating operating systems and programs from each other, but there is always an opening for these side-channel attacks on systems that share resources, said Alex Stamos, a partner with security consultancy iSEC Partners. "It's going to be a whole new class of bugs that people are going to have to fix in the next five years."
His company has worked with a number of clients interested in cloud computing, but only if they can be assured that no one else is sharing the same machine. "I'm guessing the cloud-computing providers are going to be pushed by their clients to be able to provide physical machines."
Amazon wasn't quite ready to talk about side-channel attacks Thursday. "We take all security claims very seriously and are aware of this research," a spokeswoman said. "We are investigating and will post updates to our security center."
Sign up for CIO Asia eNewsletters.