Those of you who read my Blog post about MBNA and 3D secure will know I am an MBNA Visa card customer. MBNA provide their cardholders with a comprehensive online banking solution. You can review your recent transactions, recent statements, transfer balances and even view your PIN online. Recently, MBNA made some updates to their site, modifying the login process so it is now a two step process.

This change appears to be an attempt to improve usability on the site by simplifying the log-in process. The website  provides a "Where do I enter my password?" link giving MBNA's reasons for a two-step login process, reasons which I believe are misguided.

MBNA say the new two-step login process will better safeguard the privacy and security of their customers personal information. These changes in fact compromise the security of their customers and provide scope for denial of service attacks. Here, I'm going to show you why.

The first step in the log-in process where you enter your username. Here we encounter the first problem - if you enter an incorrect username you get a message saying that the username does not match their records. Unfortunately, this means that the system can be used to find valid usernames of MBNA customers.

After entering a valid username you are presented with the password entry screen.

If an incorrect password is entered then this is indicated to the user.

Now we encounter problem number two - MBNA implement an invalid login attempts policy by which accounts are locked after 3 invalid login attempts. This itself is not the problem but combined with the ability to determine valid usernames it becomes a problem.

The invalid login attempts will prevent an attacker from carrying out a brute force attack to find the password for a cardholders username but it does leave MBNA open to a type of denial of service attack. For example, an attacker could determine a list of valid usernames for MBNA cardholders and then proceed to make three invalid login attempts for each username, locking out the accounts in the process.

The lesson is simple - when securing these systems think about the malicious mind. It is good usability practice to return useful error messages, however the error message need only be useful to the point of correcting the users error. In the MBNA example there is no logic in having a second step. It does not provide any benefit to the customer in terms of security or data protection. I would also argue that it does not provide any benefits in terms of usability as the user now has to deal with two screens, two page loads and has an extra click to submit each form.

The username and password should be entered in the same form i.e. a single step sign in process. An informative error message such as "The username or password is incorrect." can then be displayed when an invalid username or password is entered. In this way the user benefits from the usability practices behind returning useful error messages however an attacker gains no extra knowledge to help compromise the system.

Dave

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A very serious vulnerability in osCommerce was brought to our attention on November 13th. The vulnerability allows an attacker to bypass the authentication mechanism and gain access to the admin pages.

I have held off on blogging about this until now as I did not feel it was appropriate. It was a difficult decision to make, on one hand I want to inform those running osCommerce so they can secure their systems but by blogging about the issue I am also highlighting it to potential attackers.



I would like to discuss the vulnerability and how it works but we'll leave that for another time. For those of you running osCommerce you can find information about the vulnerability on the osCommerce forums and also on the powersellers forum.

There are a number of suggested solutions and patches but based on my research the simplest thing to do is to protect the admin directory using .htaccess-based authentication.

Dave

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Related Blog Posts:

• CubeCart neglect to inform their customers of critical vulnerability
  
• Details of the Twitter attack revealed
• Exploiting a back-office application with CSRF