zonbron |
26 september 2011 15:06 |
Citaat:
25th September 2011 #
Logging out of Facebook is not enough
Dave Winer wrote a timely piece this morning about how Facebook is scaring him since the new API allows applications to post status items to your Facebook timeline without a users intervention. It is an extension of Facebook Instant and they call it frictionless sharing. The privacy concern here is that because you no longer have to explicitly opt-in to share an item, you may accidentally share a page or an event that you did not intend others to see.
The advice is to log out of Facebook. But logging out of Facebook only de-authorizes your browser from the web application, a number of cookies (including your account number) are still sent along to all requests to facebook.com. Even if you are logged out, Facebook still knows and can track every page you visit. The only solution is to delete every Facebook cookie in your browser, or to use a separate browser for Facebook interactions.
Here is what is happening, as viewed by the HTTP headers on requests to facebook.com. First, a normal request to the web interface as a logged in user sends the following cookies:
Note: I have both fudged the values of each cookie and added line wraps for legibility
Cookie:
(CODE)
The request to the logout function will then see this response from the server, which is attempting to unset the following cookies:
Set-Cookie:
(CODE)
To make it easier to see the cookies being unset, the names are in italics. If you compare the cookies that have been set in a logged in request, and compare them to the cookies that are being unset in the logout request, you will quickly see that there are a number of cookies that are not being deleted, and there are two cookies (locale and lu) that are only being given new expiry dates, and three new cookies (W, fl, L) being set.
Now I make a subsequent request to facebook.com as a 'logged out' user:
Cookie:
(CODE)
The primary cookies that identify me as a user are still there (act is my account number), even though I am looking at a logged out page. Logged out requests still send nine different cookies, including the most important cookies that identify you as a user
This is not what 'logout' is supposed to mean - Facebook are only altering the state of the cookies instead of removing all of them when a user logs out.
With my browser logged out of Facebook, whenever I visit any page with a Facebook like button, or share button, or any other widget, the information, including my account ID, is still being sent to Facebook. The only solution to Facebook not knowing who you are is to delete all Facebook cookies.
You can test this for yourself using any browser with developer tools installed. It is all hidden in plain sight.
An Experiment
This brings me back to a story that I have yet to tell. A year ago I was screwing around with multiple Facebook accounts as part of some development work. I created a number of fake Facebook accounts after logging out of my browser. After using the fake accounts for some time, I found that they were suggesting my real account to me as a friend. Somehow Facebook knew that we were all coming from the same browser, even though I had logged out.
There are serious implications if you are using Facebook from a public terminal. If you login on a public terminal and then hit 'logout', you are still leaving behind fingerprints of having been logged in. As far as I can tell, these fingerprints remain (in the form of cookies) until somebody explicitly deletes all the Facebook cookies for that browser. Associating an account ID with a real name is easy - as the same ID is used to identify your profile.
Facebook knows every account that has accessed Facebook from every browser and is using that information to suggest friends to you. The strength of the 'same machine' value in the algorithm that works out friends to suggest may be low, but it still happens. This is also easy to test and verify.
I reported this issue to Facebook in a detailed email and got the bounce around. I emailed somebody I knew at the company and forwarded the request to them. I never got a response. The entire process was so flaky and frustrating that I haven't bothered sending them two XSS holes that I have also found in the past year. They really need to get their shit together on reporting privacy issues, I am sure they take security issues a lot more seriously.
The Rise of Privacy Awareness
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nikcub
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Tip..., verwijder STEEDS uw LSO-cookies, gebruik Firefox+ADD ON Better Privacy.
Citaat:
If you want to minimize your exposure to the grid, it may be time to say good-bye to Facebook and Google+, especially if you are politically active.
Start by deactivating your Facebook and Google+ accounts and deleting their cookies on your computer.
How to delete cookies...
Most cookies are easy to delete. Just pick your browser from the choices below and follow the instructions. If your browser isn't listed, please contact us.
You probably have Adobe Local Shared Objects on your computer, also known as LSOs or Flash cookies. Generally you can't delete them with browsers controls, but Adobe's website offers tools to control Flash cookies on your computer. Users of the Firefox browser can also get an add-on to detect and delete Flash cookies.
Windows PC
* Google Chrome
* Internet Explorer 9
* Internet Explorer 8
* Internet Explorer 7.x
* Internet Explorer (all other versions)
* AOL
* Mozilla
* Mozilla Firebird 0.7
* Mozilla Firefox
* Netscape Navigator 7.x
* Netscape Navigator 6.x
* Netscape Navigator 4.x
* Opera
* Deepnet Explorer 1.1+
...
aboutcookies
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