Researchers Reverse Engineer Dropbox Client

A paper presented at USENIX demonstrates how two researchers managed to reverse engineer Dropbox.

Researchers have cracked open cloud storage service Dropbox, reverse engineering the encryption protecting the client in order to open it up to further security analysis.

The engineers, Dhiru Kholia of Openwall and Przemyslaw Wegrzyn of CodePainters, also managed to demonstrate how to use code-injection techniques to intercept SSL data, essentially hijacking Dropbox communication, as well as bypass two-factor authentication used to protect accounts. The two researchers presented a paper on their work at the recent USENIX Security Symposium.

“Reversing Dropbox is the main focus of our paper,” Kholia told Threatpost. “The attacks are just side-effects.”

A Dropbox spokesperson said in an email to Threatpost that the duo’s findings do not represent a vulnerability in Dropbox. “In the case outlined here, the user’s computer would first need to have been compromised in such a way that it would leave the entire computer, not just the user’s Dropbox, open to attacks across the board,” the spokesman said.

Kholia concurred that hijacking a Dropbox client first requires hacking an existing vulnerability on the target user’s machine, which can be executed remotely.

“We believe that our biggest contribution is to open up the Dropbox platform to further security analysis and research,” the researchers wrote in their paper. “Dropbox will/should no longer be a black box.”

The research reveals how the internal API used by the Dropbox client works. Using a number of techniques, Kholia and Wegrzyn were able to decompile the Dropbox client source code and examine it. While previous work exists in this field, it’s applicable only to older versions of Dropbox, the researchers said. Patches have been applied by the Dropbox team that prevented them from applying previously successful research in this case.

In addition, they were able to use Reflective DLL injection and LD_PRELOAD on Windows and Linux respectively to intercept SSL traffic.

“Once we are able to execute arbitrary code in Dropbox client context, we patch all SSL objects and are able to snoop on the data before it has been encrypted (on sending side) and after it has been decrypted (on receiving side),” the paper said. “This is how we intercept SSL data. We have successfully used the same technique on multiple commercial Python applications.”

They also learned that the two-factor authentication used to access Dropbox on the Web isn’t supported on the client and the client can be accessed with a  value known as host_ID, which they were able to gain.

While the team plans further research into Dropbox security and encourages the security community to take its shots, they acknowledge the client’s security is a constantly moving target, one that has remained fairly safe.

“Overall, Dropbox is just fine,” Kholia said. “There is nothing to worry about. We are still using and loving it.”

Image courtesy JeanbaptisteM.

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