According to the Oracle Java API, the ``++HttpServletRequest.getRequestedSessionId()++`` method:

____
Returns the session ID specified by the client. This may not be the same as the ID of the current valid session for this request. If the client did not specify a session ID, this method returns null.

____

The session ID it returns is either transmitted in a cookie or a URL parameter so by definition, nothing prevents the end-user from manually updating the value of this session ID in the HTTP request. 


Here is an example of a updated HTTP header:

----
GET /pageSomeWhere HTTP/1.1
Host: webSite.com
User-Agent: Mozilla/5.0
Cookie: JSESSIONID=Hacked_Session_Value'''">
----

Due to the ability of the end-user to manually change the value, the session ID in the request should only be used by a servlet container (E.G. Tomcat or Jetty) to see if the value matches the ID of an an existing session. If it does not, the user should be considered  unauthenticated. Moreover, this session ID should never be logged as is but using a one-way hash to prevent hijacking of active sessions.


== Noncompliant Code Example

----
if(isActiveSession(request.getRequestedSessionId()) ){
  ...
}
----


== See

* https://www.owasp.org/index.php/Top_10-2017_A2-Broken_Authentication[OWASP Top 10 2017 Category A2] - Broken Authentication
* http://cwe.mitre.org/data/definitions/807[MITRE, CWE-807] - Reliance on Untrusted Inputs in a Security Decision
* https://www.sans.org/top25-software-errors/#cat3[SANS Top 25] - Porous Defenses


