Session Fixation Example

I usually see session fixation vulnerabilities with Java web applications. Just recently I found a ColdFusion application vulnerable to session fixation. This nasty security hole greatly increases the risk that users will have their sessions hijacked. Once an attacker has hijacked a session, he can view any data or perform any action that the legitimate user can. 

Both HP WebInspect and Burp Pro's active scanner failed to find this vulnerability. Testing for session fixation is quite easy to do, so I ran a quick test for it manually.

When testing for session fixation, I normally use two different browsers: IE and Firefox in this example. If the login page for an application is https://someapp.com/login, testing for session fixation consists of the following steps:

1. Launch Firefox and navigate directly to the login page.

2. Inspect the cookie(s) assigned by the application. For a Java web app, a JSESSIONID cookie will normally be set. In the case of ColdFusion, you normally see CFID and CFTOKEN cookies.

3. Copy the session ID from the cookie.

4. Construct a special URL that contains the session ID.
For Java, it looks like this:
https://someapp.com/login.jsp;jsessionid=[sessid]
For ColdFusion, it looks like this:
https://someapp.com/login.cfm?cfid=[cfid]&cftoken=[cftoken]

5. Open IE and configure it to run through a proxy (Burp, Paros, Fiddler2, etc.).

6. Paste the special URL into the IE address bar and hit Enter (this step simulates a victim clicking on a link in an email or Internet post).

7. Observe the HTTP response from the server. Is there a "Set-Cookie" header? If so, what is the session ID? You have a problem if it's the same value that's in the URL. On the other hand, you're probably okay if the value is different.

The ColdFusion site I tested was handling the situation even more poorly than usual. It was not necessary to visit the site initially to obtain legitimate session IDs from the server, so steps 1-3 above weren't even needed. An attacker could make up *any* 6 digit value for "cfid" and *any* 8 digit value for "cftoken", then embed these made-up values in the malicious URL, and the application happily accepted them.

The server responded by assigning CFID and CFTOKEN cookies based on the made-up values as illustrated below.

The URL of the request was:
https://someapp.com/login.cfm?cfid=999555&cftoken=29292929

And the HTTP response contained the following headers:
Set-Cookie: CFID=999555; path=/; Secure
Set-Cookie: CFTOKEN=29292929; path=/; Secure