Testing for Credentials Transported over an Encrypted Channel (OTG-AUTHN-001)

Brief Summary
Testing for credentials transport means to verify that the user's authentication data are transferred via an encrypted channel to avoid being intercepted by malicious users. The analysis focuses simply on trying to understand if the data travels unencrypted from the web browser to the server, or if the web application takes the appropriate security measures using a protocol like HTTPS. The HTTPS protocol is built on TLS/SSL to encrypt the data that is transmitted and to ensure that user is beinging sent towards the desired site. Clearly, the fact that traffic is encrypted does not necessarily mean that it's completely safe. The security also depends on the encryption algorithm used and the robustness of the keys that the application is using, but this particular topic will not be addressed in this section. For a more detailed discussion on testing the safety of TLS/SSL channels you can refer to the chapter Testing for SSL-TLS (OWASP-CM-001). Here, the tester will just try to understand if the data that users put into web forms, for example, in order to log into a web site, are transmitted using secure protocols that protect them from an attacker or not. To do this we will consider various examples.

Description of the Issue
Nowadays, the most common example of this issue is the login page of a web application. The tester should verify that user's credentials are transmitted via an encrypted channel. In order to log into a web site, usually, the user has to fill a simple form that transmits the inserted data with the POST method. What is less obvious is that this data can be passed using the HTTP protocol, that means in a non-secure way, or using HTTPS, which encrypts the data. To further complicate things, there is the possibility that the site has the login page accessible via HTTP (making us believe that the transmission is insecure), but then it actually sends data via HTTPS. This test is done to be sure that an attacker cannot retrieve sensitive information by simply sniffing the net with a sniffer tool.

Black Box testing and example
In the following examples we will use WebScarab in order to capture packet headers and to inspect them. You can use any web proxy that you prefer.

Case study: Sending data with POST method through HTTP

Suppose that the login page presents a form with fields User, Pass, and the Submit button to authenticate and give access to the application. If we look at the header of our request with WebScarab, we get something like this: POST http://www.example.com/AuthenticationServlet HTTP/1.1 Host: www.example.com User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; it; rv:1.8.1.14) Gecko/20080404 Accept: text/xml,application/xml,application/xhtml+xml Accept-Language: it-it,it;q=0.8,en-us;q=0.5,en;q=0.3 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Connection: keep-alive Referer: http://www.example.com/index.jsp Cookie: JSESSIONID=LVrRRQQXgwyWpW7QMnS49vtW1yBdqn98CGlkP4jTvVCGdyPkmn3S! Content-Type: application/x-www-form-urlencoded Content-length: 64

delegated_service=218&User=test&Pass=test&Submit=SUBMIT

From this example the tester can understand that the POST sends the data to the page www.example.com/AuthenticationServlet simply using HTTP. So, in this case, data are transmitted without encryption and a malicious user could read our username and password by simply sniffing the net with a tool like Wireshark.

Case study: Sending data with POST method through HTTPS

Suppose that our web application uses the HTTPS protocol to encrypt data we are sending (or at least for those relating to the authentication). In this case, trying to access the login page and to authenticate, the header of our POST request would be similar to the following:

POST https://www.example.com:443/cgi-bin/login.cgi HTTP/1.1 Host: www.example.com User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; it; rv:1.8.1.14) Gecko/20080404 Accept: text/xml,application/xml,application/xhtml+xml,text/html Accept-Language: it-it,it;q=0.8,en-us;q=0.5,en;q=0.3 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Connection: keep-alive Referer: https://www.example.com/cgi-bin/login.cgi Cookie: language=English; Content-Type: application/x-www-form-urlencoded Content-length: 50

Command=Login&User=test&Pass=test

We can see that the request is addressed to www.example.com:443/cgi-bin/login.cgi using the HTTPS protocol. This ensures that our data are sent through en encrypted channel and that they are not readable by other people.

Case study: sending data with POST method via HTTPS on a page reachable via HTTP

Now, suppose to have a web page reachable via HTTP and that then only data sent from the authentication form are shipped via HTTPS. This means that our data is transmitted in a secure way through encryption. This situation occurs, for example, when we are on a portal of a big company that offers various information and services publicly available, without identification, but which has also a private section accessible from the home page through a login. So when we try to login, the header of our request will look like the following example:

POST https://www.example.com:443/login.do HTTP/1.1 Host: www.example.com User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; it; rv:1.8.1.14) Gecko/20080404 Accept: text/xml,application/xml,application/xhtml+xml,text/html Accept-Language: it-it,it;q=0.8,en-us;q=0.5,en;q=0.3 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Connection: keep-alive Referer: http://www.example.com/homepage.do Cookie: SERVTIMSESSIONID=s2JyLkvDJ9ZhX3yr5BJ3DFLkdphH0QNSJ3VQB6pLhjkW6F Content-Type: application/x-www-form-urlencoded Content-length: 45

User=test&Pass=test&portal=ExamplePortal

We can see that our request is addressed to www.example.com:443/login.do using HTTPS. But if we have a look at the referer field in the header (the page from which we came), it is www.example.com/homepage.do and is accessible via simple HTTP. So, in this case, we have no lock inside our browser window that tells us that we are using a secure connection, but, in reality, we are sending data via HTTPS. This ensures us that no other people can read the data that we are sending.

Case study: Sending data with GET method through HTTPS

In this last example, suppose that the application transfers data using the GET method. This method should never be used in a form that transmits sensitive data such as username and password, because they are displayed in clear in the URL and this entails a whole set of security issues. So this example is purely demonstrative, but, in reality, it is strongly suggested to use the POST method instead. This is because when the GET method is used, the url that it requests is easily available from, for example, the server logs exposing your sensitive data to information leakage.

GET https://www.example.com/success.html?user=test&pass=test HTTP/1.1 Host: www.example.com User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; it; rv:1.8.1.14) Gecko/20080404 Accept: text/xml,application/xml,application/xhtml+xml,text/html Accept-Language: it-it,it;q=0.8,en-us;q=0.5,en;q=0.3 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Connection: keep-alive Referer: https://www.example.com/form.html If-Modified-Since: Mon, 30 Jun 2008 07:55:11 GMT If-None-Match: "43a01-5b-4868915f"

You can see that the data is transferred in clear text in the URL and not in the body of the message as before. But we must consider that TLS/SSL is a level 5 protocol, a lower level than HTTP, then the whole HTTP package is still encrypted and the URL is unreadable to an attacker. It is not a good practice to use the GET method in these cases, because the information contained in the URL can be stored in many servers such as proxy and web servers, leaking the privacy of the user's credentials.

Gray Box testing and example
Talk with the developers of the application and try to understand if they are aware of differences between HTTP and HTTPS protocols and why they should use the HTTPS for sensitive information transmissions. Then, check with them if HTTPS is used in every sensitive transmission, like those in login pages, to prevent unauthorized users to read the data.