Reviewing code for Cross-Site Request Forgery issues - Revision history

Thomas Herlea: Added navigation to facilitate sequential reading online

2010-09-09T16:35:08Z

Added navigation to facilitate sequential reading online

KirstenS at 20:08, 4 March 2009

2009-03-04T20:08:39Z

KirstenS: /* How to Locate the Potentially Vulnerable Code */

2009-02-11T01:21:17Z

‎How to Locate the Potentially Vulnerable Code

KirstenS: /* How They Work */

2009-02-11T01:21:07Z

‎How They Work

KirstenS: /* User Interaction */

2009-01-28T14:26:40Z

‎User Interaction

KirstenS: /* Good Patterns & procedures to prevent CSRF */

2009-01-28T14:26:09Z

‎Good Patterns & procedures to prevent CSRF

KirstenS: /* How to Locate the Potentially Vulnerable Code */

2009-01-28T14:23:46Z

‎How to Locate the Potentially Vulnerable Code

KirstenS: /* How They Work: */

2009-01-28T14:22:43Z

‎How They Work:

KirstenS: /* Overview */

2009-01-28T14:21:12Z

‎Overview

KirstenS: /* Good Patterns & procedures to prevent CSRF */

2009-01-13T17:01:48Z

‎Good Patterns & procedures to prevent CSRF

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-[[OWASP Code Review Guide Table of Contents]]__TOC__
+{{LinkBar
 ==Overview==
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 [[CSRF Guard]]
 [[Category:OWASP Code Review Project]]
 [[Category:Identity Theft]]

← Older revision		Revision as of 20:08, 4 March 2009
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	See the [[:Category:OWASP Testing Project\|OWASP Testing Guide]] article on how to [[Testing for CSRF (OWASP-SM-005)\|Test for CSRF]] Vulnerabilities.		See the [[:Category:OWASP Testing Project\|OWASP Testing Guide]] article on how to [[Testing for CSRF (OWASP-SM-005)\|Test for CSRF]] Vulnerabilities.
−	~~[[Category:FIXME\|I think both the Introduction and How They Work sections here need to be deleted, since this is duplicate information]]~~

	== Introduction ==		== Introduction ==

← Older revision		Revision as of 01:21, 11 February 2009
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	By checking the page rendering we need to see if any unique identifiers are appended to the links rendered by the application in the user's browser. If there is no unique identifier relating to each HTTP request to tie a HTTP request to the user, we are vulnerable. Session ID is not enough, as the session ID shall be sent anyway if a user clicks on a rogue link, as the user is authenticated already.		By checking the page rendering we need to see if any unique identifiers are appended to the links rendered by the application in the user's browser. If there is no unique identifier relating to each HTTP request to tie a HTTP request to the user, we are vulnerable. Session ID is not enough, as the session ID shall be sent anyway if a user clicks on a rogue link, as the user is authenticated already.
−

	===Transaction Drive Thru===		===Transaction Drive Thru===

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 An Example below of a HTTP POST to a ticket vendor to purchase a number of tickets.
   POST http://TicketMeister.com/Buy_ticket.htm HTTP/1.1
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   Cookie: JSPSESSIONID=34JHURHD894LOP04957HR49I3JE383940123K
   ticketId=ATHX1138&to=PO BOX 1198 DUBLIN 2&amount=10&date=11042008
 The response of the vendor is to acknowledge the purchase of the tickets:

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 ==User Interaction==
-Upon committing to a transaction, such as fund transfer, display an additional decision to the user ,such as a requirement for one’s password to be entered and verified prior to the transaction taking place. A CSRF attacker would not know the password of the user and therefore the transaction could not be committed via a stealth CSRF attack.
+Upon committing to a transaction, such as fund transfer, display an additional decision to the user, such as a requirement for one’s password to be entered and verified prior to the transaction taking place. A CSRF attacker would not know the password of the user and therefore the transaction could not be committed via a stealth CSRF attack.
 ==Related Articles==

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 '''Any application that accepts HTTP requests from an authenticated user without having some control to verify that the HTTP request is unique to the user's session.''' (Nearly all web applications!!). Session ID is not in scope here as the rogue HTTP request shall also contain a valid session ID, as the user is authenticated already.
-==Good Patterns & procedures to prevent CSRF==
+==Good Patterns and procedures to prevent CSRF==
 Checking if the request has a valid session cookie is not enough, we need check if a unique identifier is sent with every HTTP request sent to the application. CSRF requests WON'T have this valid unique identifier. The reason CSRF requests won't have this unique request identifier is the unique ID is rendered as a hidden field on the page and is appended to the HTTP request once a link/button press is selected. The attacker will have no knowledge of this unique ID, as it is random and rendered dynamically per link, per page.
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 # A unique ID is appended to each link/form on the requested page prior to being displayed to the user.
 # Maintaining a list of unique IDs in the user session, the application checks if the unique ID passed with the HTTP request is valid for a given request.  if the unique ID passed with the HTTP request is valid for a given request.
 # If the unique ID is not present, terminate the user session and display an error to the user.
 ==User Interaction==

← Older revision		Revision as of 14:23, 28 January 2009
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	This issue is simple to detect, but there may be compensating controls around the functionality of the application which may alert the user to a CSRF attempt. As long as the application accepts a well formed HTTP request and the request adheres to some business logic of the application CSRF shall work (From now on we assume the target user is logged into the system to be attacked).		This issue is simple to detect, but there may be compensating controls around the functionality of the application which may alert the user to a CSRF attempt. As long as the application accepts a well formed HTTP request and the request adheres to some business logic of the application CSRF shall work (From now on we assume the target user is logged into the system to be attacked).

−	By checking the page rendering we need to see if any unique identifiers are appended to the links rendered by the application in the user's browser. If there is no unique identifier relating to each HTTP request to tie a HTTP request to the user, we are vulnerable. Session ID is not enough as the session ID shall be sent anyway if a user clicks on a rogue link as the user is authenticated already.	+	By checking the page rendering we need to see if any unique identifiers are appended to the links rendered by the application in the user's browser. If there is no unique identifier relating to each HTTP request to tie a HTTP request to the user, we are vulnerable. Session ID is not enough, as the session ID shall be sent anyway if a user clicks on a rogue link, as the user is authenticated already.

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 In effect CSRF attacks are used by an attacker to make a target system perform a function (Funds Transfer, Form submission etc..) via the target’s browser without the knowledge of the target user, at least until the unauthorized function has been committed. A primary target is the exploitation of “ease of use” features on web applications (One-click purchase), for example.
-==How They Work:==
+==How They Work==
 CSRF attacks work by sending a rogue HTTP request from an authenticated user's browser to the application, which then commits a transaction without authorization given by the target user. As long as the user is authenticated and a meaningful HTTP request is sent by the user’s browser to a target application, the application does not know if the origin of the request is a valid transaction or a link clicked by the user (that was, say, in an email) while the user is authenticated to the application. So, for example, using CSRF, an attacker makes 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.

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 ==Overview==
-[[CSRF]] is an attack which forces an end user to execute unwanted actions on a web application in which he/she is currently authenticated. With a little help of social engineering (like sending a link via email/chat), an attacker may force the users of a web application to execute actions of the attackers choosing. A successful CSRF exploit can compromise end user data and operation in the case of a normal user. If the targeted end user is the administrator account, this can compromise the entire web application.
+[[CSRF]] is an attack which forces an end user to execute unwanted actions on a web application in which he/she is currently authenticated. With a little help of social engineering (like sending a link via email/chat), an attacker may force the users of a web application to execute actions of the attacker's choosing. A successful CSRF exploit can compromise end user data and operation in the case of a normal user. If the targeted end user is the administrator account, this can compromise the entire web application.
 ==Related Security Activities==

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 ==Good Patterns & procedures to prevent CSRF==
-So checking if the request has a valid session cookie is not enough, we need check if a unique identifier is sent with every HTTP request sent to the application.
+Checking if the request has a valid session cookie is not enough, we need check if a unique identifier is sent with every HTTP request sent to the application. CSRF requests WON'T have this valid unique identifier. The reason CSRF requests won't have this unique request identifier is the unique ID is rendered as a hidden field on the page and is appended to the HTTP request once a link/button press is selected. The attacker will have no knowledge of this unique ID, as it is random and rendered dynamically per link, per page.
-#A list is complied prior to delivering the page to the user. The list contains all valid unique IDs generated for all links on a given page. The unique ID could be derived from a secure random generator such as SecureRandom for J2EE.
+# A list is complied prior to delivering the page to the user. The list contains all valid unique IDs generated for all links on a given page. The unique ID could be derived from a secure random generator such as SecureRandom for J2EE. .
-#A unique ID is appended to each link/form on the requested page prior to being displayed to the user.
+# A unique ID is appended to each link/form on the requested page prior to being displayed to the user.
-#Maintaining a list of unique IDs in the user session, the application checks if the unique ID passed with the HTTP request is valid for a given request.
+# Maintaining a list of unique IDs in the user session, the application checks if the unique ID passed with the HTTP request is valid for a given request.  if the unique ID passed with the HTTP request is valid for a given request.
-#If the unique ID is not present, terminate the user session and display an error to the user.
+# If the unique ID is not present, terminate the user session and display an error to the user.
-===User Interaction===
+==User Interaction==
-Upon committing to a transaction such as fund transfer display an additional decision to the user such as a requirement for ones password to be entered and verified prior to the transaction taking place.
+Upon committing to a transaction, such as fund transfer, display an additional decision to the user ,such as a requirement for one’s password to be entered and verified prior to the transaction taking place. A CSRF attacker would not know the password of the user and therefore the transaction could not be committed via a stealth CSRF attack.
 ==Related Articles==