Reviewing code for Cross-Site Request Forgery issues

OWASP Code Review Guide Table of Contents

Introduction
Cross-Site Request Forgery (CSRF) attacks are considered useful if the attacked knows the target is authenticated to a web based system. They dont work unless the target is logged into the system and therefore have a small attack footprint. In effect CSRF attacks are used by an attacker to make a target system perform a function via the targets browser without knowledge of the target user, at least until the unauthorised function has been comitted.

How they work:
See:
 * 1) http://www.owasp.org/index.php/CSRF_Guard
 * 2) http://www.owasp.org/index.php/Cross-Site_Request_Forgery

for a more detailed explaination but the main issue is the sending of a rogue HTTP request from an authenticated users browser to the application which shall commit a transaction without authorisation given by the target user. As long as the user is authenticated and a menaingful HTTP request is sent by the users browser to a target application the application does not know if origin of the request be it a valid transaction or a link clicked by the user (that was say, in an email) whilst the user is authenticated to the applications. So, as an example, using CSRF an attacker make the victim perform actions that they didn't intend to, such as logout, purchase item, change account information, or any other function provided by the vulnerable website.