Web Search History Information Leakage

Back in February, I re-discovered a small flaw in Google Search: result personalization leaks the list of results you clicked on. This leak was already known and mentioned in a paper by Castelluccia et al., but several features added by Google made it critical.

  • First there is the possibility (for web search history users) to only view result that have already been visited (visit http://www.google.com/webhp?tbs=whv:1).
  • Second,  with Google Instant it is possible to view visited links quickly without living a trace in the victim Web Search history (the attack is not-destructive).
  • Third, when Google display previously visited search results, it used to provide the query that led to the results searching when he clicked on the result, thus the attacker knew which keywords the victim was usually searching for and could have enter these keywords in a search box to get new results which will suggest new keywords to type and so forth and so on…

The third point has been addressed by Google very recently, when they introduced the new interface with the black top bar.
Vincent Verdot and I wrote a paper about this flaw. In order to conduct an experiment, we’ve been working on a proof of concept and an evaluation tool that we used to gather results.

Proof of concept based on Firesheep

This proof of concept is based on Firesheep (I just added a module and modify the attack launched when a SID cookie was captured). Firesheep is only working with the latest version of Firefox 3.6, do not expect to run it on Firefox 5.
With our version of Firesheep, when a Google SID cookie is captured, the account name appears in the Firesheep sidebar. Double clicking on it starts the attack; double clicking again displays the retrieved list of visited links.

The Evaluation tool

We also designed a Firefox extension which downloads your web search history on your computer, issue a couple of search queries (mostly searching for extensions like: « .com, .fr, .us, .html, www, … ») and see how many clicked links can be retrieved.
We’ve run this experiment with a dozen of account and sent the result to Google. We’ll soon publish the paper as a technical report.

How to protect your Click History

We’ve been in contact with Google Security Team who is working on a fix that should soon be deployed. In the meantime, make sure you’re not logged in your Google account when you’re connected on an unsecured network.
If you do not use Web Search History you may also purge it and disable the feature (visit https://www.google.com/history).
Also, TrackMeNot and Unsearch will reduce the exposition of your click history.

 

Running the Test

If you want to run the test 5 minutes:

  • A Google Account with Web Search History enabled. To check that you activated it, visit https://www.google.com/history; if it asks you to turn on the feature, then you cannot help here. Thanks anyway for trying.
  • Install this Firefox extension (http://unsearcher.org/Test%20Flaw/ad@monitor.xpi), download it and then drag it and drop it in Firefox. Once the extension has been installed, you should restart Firefox.
  • Modify your Google Search preferences (http://www.google.com/preferences?hl=en) to disable “Google Instant” and set the number of returned result to 100 (instead of 10).
  • Sign out and Sign in again on Google.com.
  • In Firefox, click on “Tools-> ADMONITOR-> History”. A first message should appear to inform you that the extension is about to extract your search History. Click on OK and do not close the Firefox window.
  • After five minutes, another message will be prompted to inform you that the test is finished. It’ll tell you where you can find the generated file. A Firefox window should have open (not necessarily taking the focus). You can send me the content of this window via e-mail and we’ll integrate it in our experiment results.
  • You can remove the generated files and uninstall the sid@testextension.

Thanks for helping us.