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

This article is part of the new OWASP Testing Guide v4.

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   https://www.owasp.org/index.php/OWASP_Testing_Guide_v4_Table_of_Contents
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Summary

Testing for credentials transport means verifying 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 being 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 refer to the chapter Testing for Weak SSL/TLS. Here, the tester will just try to understand if the data that users put in to web forms in order to log in to a web site, are transmitted using secure protocols that protect them from an attacker.

Nowadays, the most common example of this issue is the log in page of a web application. The tester should verify that user's credentials are transmitted via an encrypted channel. In order to log in to a web site, the user usually has to fill a simple form that transmits the inserted data to the web application with the POST method. What is less obvious is that this data can be passed using the HTTP protocol, which transmits the data in a non-secure, clear text form, or using the HTTPS protocol, which encrypts the data during the transmission. 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 network with a sniffer tool.

How to Test

Black Box testing

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.

Example 1: 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 headers of our request with WebScarab, we can 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 request sends the data to the page www.example.com/AuthenticationServlet using HTTP. Sothe data is transmitted without encryption and a malicious user could intercept the username and password by simply sniffing the network with a tool like Wireshark.

Example 2: Sending data with POST method through HTTPS

Suppose that our web application uses the HTTPS protocol to encrypt the data we are sending (or at least for transmitting sensitive data like credentials). In this case, when logging on to the web application 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 credentials are sent using an encrypted channel and that the credentials are not readable by a malicious user using a sniffer.

Example 3: sending data with POST method via HTTPS on a page reachable via HTTP

Now, imagine having a web page reachable via HTTP and that only data sent from the authentication form are transmitted via HTTPS. This situation occurs, for example, when we are on a portal of a big company that offers various information and services that are publicly available, without identification, but the site also has a private section accessible from the home page when users log in. So when we try to log in, the header of our request will look like the following example:

POST http://www.example.com/homepage.do
Host: http://www.example.com/homepage.do
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-header (the page from which we came), it is www.example.com/homepage.do and is accessible via simple HTTP. Although we are sending data via HTTPS, this deployment can allow SSLStrip attacks (a type of Man-in-the-middle attack)

Example 4: 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 the data is displayed in clear text in the URL and this causes a whole set of security issues. For example, the URL that is requested is easily available from the server logs or from your browser history, which makes your sensitive data retrievable for unauthorized persons. So this example is purely demonstrative, but, in reality, it is strongly suggested to use the POST method instead.

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 request as before. But we must consider that SSL/TLS is a level 5 protocol, a lower level than HTTP, so the whole HTTP packet is still encrypted making the URL unreadable to a malicious user using a sniffer. Nevertheless as stated before, it is not a good practice to use the GET method to send sensitive data to a web application, because the information contained in the URL can be stored in many locations such as proxy and web server logs.

Gray Box testing

Speak with the developers of the web application and try to understand if they are aware of the differences between HTTP and HTTPS protocols and why they should use HTTPS for transmitting sensitive information. Then, check with them if HTTPS is used in every sensitive request, like those in log in pages, to prevent unauthorized users to intercept the data.

Tools

• WebScarab
• OWASP Zed Attack Proxy (ZAP)

References

Whitepapers

• HTTP/1.1: Security Considerations - http://www.w3.org/Protocols/rfc2616/rfc2616-sec15.html
• SSL is not about encryption