Testing for Session Fixation (OWASP-SM-003)

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).

Description of the Issue
Session fixation vulnerabilities occur when: 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.
 * 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.

Furthermore, the issue described above is problematic for sites which issue a session identifier over HTTP and then redirect the user to a HTTPS login form. If the session identifier is not reissued upon authentication, the identifier may be eavesdropped and may be used by an attacker to hijack the session.

Black Box testing and example
Testing for Session Fixation vulnerabilities: The first step is to make a request to the site to be tested (example www.example.com). If we request the following: GET www.example.com We 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 We observe that the application sets a new session identifier JSESSIONID=0000d8eyYq3L0z2fgq10m4v-rt4:-1 for the client. Next, if we successfully authenticate 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 We observe 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 we know that it is possible to perform session hijacking. Result Expected: We 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 and example
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.