It was recently announced that there was a flaw identified (and since fixed) in the Verizon API that allowed access to Verizon customer email accounts. The way this worked was that there was an ID parameter with the email account’s user ID specified. If a user supplied a different user’s ID name, that user’s email account would be returned. This is known as an Insecure Direct Object Reference. It was also found that the attacker could not only read another user’s email, but also send email from that account. This could be very useful in spear phishing attacks because users are more trustful of emails from their contacts.
- Understand the parameters that are used in the application
- Use a web proxy to see the raw requests and responses for better understanding
- Create test cases for these parameters that check access to different objects to ensure authorization checks are working properly
- Implement row-based authorization to ensure the authenticated user can only see his information
The issue that is presented is that the API is not checking if the authenticated user has permission to access the specified mailbox. It would appear that it is only checking that the user is authenticated. Remember that authentication is the process of identifying who the requesting party is. Authorization is the process of determining what the authenticated user has access to. In this situation, the API should first validate that the user is authenticated, and then when a request is made for a resource (email account in this example) verify that that user is authorized to access that account before allowing it.
Unfortunately, many API’s are vulnerable to this type of attack because there is an assumption that the user can’t change the parameter values due to a lack of user interface. It is imperative that developers and QA testers both use a proxy when testing applications to be able to manipulate these types of parameters. This allows testing for unauthorized access to different objects. This is a very simple test case that should be included for every application, and not just for APIs. If you see a parameter value, make sure it is being properly tested from a security standpoint. For example, and ID field that may be an integer may get tested to make sure that the value cannot be any other type of data, but must also be checked to see if different values give access to unauthorized data.
It was also mentioned that the API didn’t use HTTPS for its communication channel. Using HTTP allows other user’s along the communication line to intercept the request and response data, potentially opening up the user to a variety of vulnerabilities. Make sure you are using the proper communication channel to protect your users in your mobile applications as well as the web applications.