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Reviewing Code for Session Integrity issues
Introduction
How to locate the potentially vulnerable code
Session Tracking/Management Techniques
HTML Hidden Field
The HTML Hidden field could be used to perform session tracking. Upon each HTTP POST request the hidden field is passed to the server identifying the user. It would be in the form of
<INPUT TYPE="hidden" NAME="user"VALUE="User001928394857738000094857hfduekjkksowie039848jej393">
Server-side code is used to perfrom validation on the VALUE in order to ensure the used is valid. This approach can only be used for POST/Form requests.
URL Rewriting
URL rewriting approaches session tracking by appending a unique id pertaining to the user at the end of the URL.
<A HREF="/smackmenow.htm?user=User001928394857738000094857hfduekjkksowie039848jej393">Click Here</A>
Cookies
Cookies were invented by netscape as a way of keeping state when using the stateless protocol HTTP. Commonly used for maintaining state but must be careful not to store any sensitive information in a cookie.
Persistant Cookies
State information and cookies
Leading Practice Patterns for Session Management/Integrity
HTTPOnly Cookie: Prevents cookie access via client side script. Not all browsers support such a directive.
Valid Session checking:
Upon any HTTP request the framework should check if the user pertaining to the HTTP request (vis session ID) is valid.
Successful Authentication:
Upon a successful login the user should be issued a new session identifier. The old session Id should be invalidated. This prevents session fixation attacks and the same browser also sharing the same session ID in a multi user environment. SOme times the session Id is per browser and the session remains valid while the browser is alive.
Logout: This also leads to the idea of why a logout button is so important. The logout button should invalidate the users session Id when it is selected.
Related Articles
http://www.owasp.org/index.php/Category:OWASP_Cookies_Database http://msdn2.microsoft.com/en-us/library/ms533046.aspx http://java.sun.com/j2ee/sdk_1.3/techdocs/api/javax/servlet/http/Cookie.html
