If you are a webpage author or use confidential information on the internet (credit card information, social security number, login credentials for paypal or banking), you might think twice the next time you log into your favorite website. I know I started paying more attention after listening to Steve Gibson's Security Now podcast titled "The Fundamentally Broken Browser Model". That title is a bit confusing, but the underlying issue is very serious. That is why I would like to further explain the issue by providing a simple example, then a real world example using facebook, and then discuss a simple solution.
First, what does Mr. Gibson mean by The Fundamentally Broken Browser Model? Well, at this years Black Hat conference, a hacker named Moxie Marlinspike gave a presentation where he talked about how he was able to capture sensitive information at a public WiFi hotspot using open tools he created. Specifically, during a 24-hour period, he intercepted 114 logins to yahoo, 50 logins to gmail, 42 to ticketmaster, 14 to rapidshare, 13 to hotmail, 9 to paypal, 9 to LinkedIn, and 3 to facebook. So how did Moxie do it? He took advantage of a common flaw of most login pages: the login pages themselves are not received by the client over SSL allowing man-in-the middle attacks to change the submit URL.
SSL (Secure Socket Layer) has been the common method for securing HTTP, but has been limited to only sensitive areas of a website for performance reasons. Sites have always protected a user's private information (usernames, passwords, credit card numbers, etc) using SSL, but to date no one has thought about actually securing the login page itself and this is a huge problem as most sites don't encrypt their login pages. Not encrypting login forms leaves it open to modification before it returns to the user.
This attack has 2 basic steps. First, the malicious user needs to be on the same network (LAN) and utilize ARP (Address Resolution Protocol) spoofing techniques to insert himself in-between connections (this is pretty scary considering how many times I have connected to restaurant, hotel, and airport WiFi hotspots). Second, a LAN user has to visit a login page that was received over a non-SSL connection.
To explain the issue better, let me use a simple example (let's leave ARP spoofing out for now). A user visits an e-commerce site http://www.eco.com. Like most sites, eco.com includes a Login link at the top. Clicking on this link takes the user to http://www.eco.com/login, which returns a simple login form in HTML.
<form method="POST" action="https://www.eco.com/login/authenticate">The user types in their username and password, clicks the Submit button, and their private information is sent encrypted over SSL. It is sent over SSL because the form's action value is set to an SSL URL (https://www.eco.com/login/authenticate). But there is one big problem. The Login link the user click was non-SSL (http://www.eco.com/login), meaning the response back to client was sent over the network as clear-text and could easily be modified by man-in-the middle attacks using ARP spoofing. A malicious user could change the form's submit URL from https://www.eco.com/login/authenticate to http://www.eco.com/login/authenticate and the user would never know it happened. There are few default clues to indicate this is happening. So a malicious user, changes the submit URL to a non-SSL URL, a user clicks Submit, and their credentials are sent as clear-text over the network.
Username: <input name="username" type="text">
Password: <input name="password" type="password">
<input value="Submit" type="submit">
Armed with this new information I wondered how some of my favorite sites handle this situation. No matter what I tried, it looked like gmail, ebay, and paypal where safe and used SSL for their login pages. So that gave me some peace of mind. However, facebook provides us with a perfect bad example.
If your like me, I type facebook in my browser and use the CRTL+ENT keyboard shortcut to fill in the rest. So I end up at http://www.facebook.com. If you are not currently logged into facebook, you are presented with the following home page that includes a form to register or login.
Again, this home page includes a login page that was sent over a non-SSL connection. As we expect, if you look at the source, you can see the HTML form does post securely to the URL https://login.facebook.com/login.php?login_attempt=1. So what do you do if you don't want to fill in a form that was received over a non-SSL connection? Fortunately, facebook also supports SSL for its home page (https://www.facebook.com), it just takes a little awareness and an extra step.
More sites need to use SSL for their login forms, and not just for when users post their credentials. At a minimum, like facebook, sites should also support SSL and ideally all login forms would automatically be requested over SSL. If you come across a site that initially does not use SSL for the login page, try and use https. If that fails then think about using a VPN solution or even a travellers router.