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Testing for Session Fixation (OTG-SESS-003)

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

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Brief Summary

When an application does not renew its session cookie(s) after a successful user authentication, it could be possible to find a session fixation vulnerability and force a user to utilize a cookie known by the attacker. In that case, an attacker could steal the user session (session hijacking).


Session fixation vulnerabilities occur when:

  • A web application authenticates a user without first invalidating the existing session ID, thereby continuing to use the session ID already associated with the user.
  • An attacker is able to force a known session ID on a user so that, once the user authenticates, the attacker has access to the authenticated session.


In the generic exploit of session fixation vulnerabilities, an attacker creates a new session on a web application and records the associated session identifier. The attacker then causes the victim to authenticate against the server using the same session identifier, giving the attacker access to the user's account through the active session.


Furthermore, the issue described above is problematic for sites that issue a session identifier over HTTP and then redirect the user to a HTTPS log in form. If the session identifier is not reissued upon authentication, the attacker can eavesdrop and steal the identifier and then use it to hijack the session.

How to Test

Black Box Testing

Testing for Session Fixation vulnerabilities:
The first step is to make a request to the site to be tested (example www.example.com). If the tester requests the following: 

GET www.example.com

They will obtain the following answer: 

HTTP/1.1 200 OK
Date: Wed, 14 Aug 2008 08:45:11 GMT
Server: IBM_HTTP_Server
Set-Cookie: JSESSIONID=0000d8eyYq3L0z2fgq10m4v-rt4:-1; Path=/; secure
Cache-Control: no-cache="set-cookie,set-cookie2"
Expires: Thu, 01 Dec 1994 16:00:00 GMT
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Content-Type: text/html;charset=Cp1254
Content-Language: en-US


The application sets a new session identifier JSESSIONID=0000d8eyYq3L0z2fgq10m4v-rt4:-1 for the client.


Next, if the tester successfully authenticates to the application with the following POST HTTPS: 

POST https://www.example.com/authentication.php HTTP/1.1
Host: www.example.com
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; it; rv:1.8.1.16) Gecko/20080702 Firefox/2.0.0.16
Accept: text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
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
Cookie: JSESSIONID=0000d8eyYq3L0z2fgq10m4v-rt4:-1
Content-Type: application/x-www-form-urlencoded
Content-length: 57

Name=Meucci&wpPassword=secret!&wpLoginattempt=Log+in


The tester observes the following response from the server: 

HTTP/1.1 200 OK
Date: Thu, 14 Aug 2008 14:52:58 GMT
Server: Apache/2.2.2 (Fedora)
X-Powered-By: PHP/5.1.6
Content-language: en
Cache-Control: private, must-revalidate, max-age=0
X-Content-Encoding: gzip
Content-length: 4090
Connection: close
Content-Type: text/html; charset=UTF-8
...
HTML data
...


As no new cookie has been issued upon a successful authentication the tester knows that it is possible to perform session hijacking.


Result Expected: The tester can send a valid session identifier to a user (possibly using a social engineering trick), wait for them to authenticate, and subsequently verify that privileges have been assigned to this cookie.


Gray Box Testing

Talk with developers and understand if they have implemented a session token renew after a user successful authentication.


Result Expected: The application should always first invalidate the existing session ID before authenticating a user, and if the authentication is successful, provide another sessionID.


Tools


References

Whitepapers


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