Mitigating Cross Site Request Forgery Attacks

The following sections describe the impact of the Cross Site Request Forgery (CSRF) attack and how to mitigate it.

How can CSRF attacks be harmful?

Cross Site Request Forgery (CSRF) attacks trick you to send a malicious request, by forcing you to execute unwanted actions on an already authenticated web browser. The session in which you logged in to the web application on the browser is used to bypass the authentication step during this attack. If you are already authenticated on the website, the site or application cannot distinguish between a forged request and a legitimate request. Therefore, it is also known as "session riding".

The attack includes maliciously tricking you to click a URL or HTML content that will consequently send a request to the website. For example:

• You send a request to an online banking application to transfer $100 to another bank account.
• An example URL including the parameters (i.e. account number and transfer amount) of a request is similar to the following: https://bank.com/transfer.do?acct=10220048&amount=100
• The attacker uses this same URL by replacing the actual account number with a malicious account number. Then the attacker disguises this URL by including it in a clickable image and sends it to you in an email with other content.
• You may unknowingly click on this URL, which will send a transfer request to the bank to transfer money to the malicious bank account.

Mitigating CSRF attacks

OWASP CSRFGuard is an OWASP flagship project that provides synchronizer token pattern-based CSRF protection in a comprehensive and customizable manner. You can use the best practices and configuration recommendations of OWASP CSRFGuard to mitigate CSRF attacks in applications hosted on the WSO2 platform. Fine-tuned configuration values of CSRFGuard increases security, based on the security requirements of the specific application.

CSRFGuard offers complete protection over CSRF scenarios by covering HTTP POST, HTTP GET as well as AJAX-based requests. You can protect forms based on HTTP POST and HTTP GET methods by injecting CSRF tokens into the “action” of the form, or by embedding a token in a hidden field.

You can protect HTTP GET requests sent as a result of resource inclusions and links can by appending a relevant token in the “href” or “src” attributes. Include these tokens manually using provided JSP tag library or by using a JavaScript based automated injection mechanism. AJAX requests are protected by injecting an additional header, which contains a CSRF token.

Configuring applications in WSO2 product to mitigate CSRF attacks

See the following for instructions on manually updating CSRF configurations in WSO2 products:

Securing web applications

Follow the steps below to secure web applications.

1. Add the following configurations in the web.xml file of your application.

   <!-- OWASP CSRFGuard context listener used to read CSRF configuration -->
   <listener>
       <listener-class>org.owasp.csrfguard.CsrfGuardServletContextListener</listener-class>
   </listener>
   <!-- OWASP CSRFGuard session listener used to generate per-session CSRF token -->
   <listener>
       <listener-class>org.owasp.csrfguard.CsrfGuardHttpSessionListener</listener-class>
   </listener>
   <!-- OWASP CSRFGuard per-application configuration property file location-->
   <context-param>
       <param-name>Owasp.CsrfGuard.Config</param-name>
       <param-value>/repository/conf/security/Owasp.CsrfGuard.properties</param-value>
   </context-param>
   <!-- OWASP CSRFGuard filter used to validate CSRF token-->
   <filter>
       <filter-name>CSRFGuard</filter-name>
       <filter-class>org.owasp.csrfguard.CsrfGuardFilter</filter-class>
   </filter>
   <!-- OWASP CSRFGuard filter mapping used to validate CSRF token-->
   <filter-mapping>
       <filter-name>CSRFGuard</filter-name>
       <url-pattern>/*</url-pattern>
   </filter-mapping>
   <!-- OWASP CSRFGuard servlet that serves dynamic token injection JavaScript (application can customize the URL pattern as required)-->
   <servlet>
       <servlet-name>JavaScriptServlet</servlet-name>
       <servlet-class>org.owasp.csrfguard.servlet.JavaScriptServlet</servlet-class>
   </servlet>
   <servlet-mapping>
       <servlet-name>JavaScriptServlet</servlet-name>
       <url-pattern>/csrf.js</url-pattern>
   </servlet-mapping>

2. Include the following JavaScriptServlet as the first JavaScript inclusion of the <head> element, in the HTML template of all pages of the application that you need to protect.

   … 
   <html>
   	<head>
   		…
   		<script type=”text/javascript” src=”/csrf.js”></script>
   
   		<!-- other JavaScript inclusions should follow “csrf.js” inclusion -->
   		<script type=”text/javascript” src=”/main.js”></script>
   		… 
   	</head>
   	<body>
   		...
   	</body>
   </html>

3. Create a CSRF configuration properties file (e.g. abc.properties) within your application, and copy the content in the <CARBON_HOME>repository/conf/security/ Owasp.CsrfGuard.Carbon.properties file to it.

4. Use the org.owasp.csrfguard.unprotected. prefix in the configuration property keys, for the relevant patterns that you need to exclude from CSRF protection. For example;

   org.owasp.csrfguard.unprotected.Default=%servletContext%/exampleAction
   org.owasp.csrfguard.unprotected.Default_1=%servletContext%/exampleAction
   org.owasp.csrfguard.unprotected.Example=%servletContext%/exampleAction/*
   org.owasp.csrfguard.unprotected.ExampleRegEx=^%servletContext%/.*Public\.do$

5.   Change the following configuration properties, to further enhance security. You may need justifiable application level requirements to change them since they will affect performance or user experience.

   Property	Description
   org.owasp.csrfguard.PRNG=SHA1PRNG	Defines the hashing algorithm used to generate the CSRF token.
   org.owasp.csrfguard.TokenLength=32	Defines the length of the CSRF token.
   org.owasp.csrfguard.action.Invalidate=org.owasp.csrfguard.action.Invalidate	Invalidates the user session, if a CSRF attack attempt was blocked by CSRFGuard.

Securing Jaggery applications

Follow the steps below to secure Jaggery applications.

1. Add the following configurations in the jaggery.conf file of your application.

    "listeners" : [
   	{
   		"class" : "org.owasp.csrfguard.CsrfGuardServletContextListener"	
   	},
   	{
   		"class" : "org.owasp.csrfguard.CsrfGuardHttpSessionListener"	
   	}
       ],
       "servlets" : [
   	{
   		"name" : "JavaScriptServlet",
   		"class" : "org.owasp.csrfguard.servlet.JavaScriptServlet"
   	}
       ],
       "servletMappings" : [
   	{
   		"name" : "JavaScriptServlet",
   		"url" : "/csrf.js"
   	}
       ],
       "contextParams" : [
   	{
   		"name" : "Owasp.CsrfGuard.Config",
   		"value" : "/repository/conf/security/Owasp.CsrfGuard.dashboard.properties"
   	}
       ]

2. Include the following JavaScriptServlet as the first JavaScript inclusion of the <head> element in the HTML template of all pages of the application that you need to protect.

   <html>
   	<head>
   		…
   		<script type=”text/javascript” src=”/csrf.js”></script>
   
   		<!-- other JavaScript inclusions should follow “csrf.js” inclusion -->
   		<script type=”text/javascript” src=”/main.js”></script>
   		… 
   	</head>
   	<body>
   		...
   	</body>
   </html>

3. Create a CSRF configuration properties file (e.g. abc.properties) within your application, and copy the content in the <CARBON_HOME>repository/conf/security/ Owasp.CsrfGuard.Carbon.properties file to it.

4. Use the org.owasp.csrfguard.unprotected. prefix in the configuration property keys, for the relevant patterns that you need to exclude from CSRF protection. For example;

   org.owasp.csrfguard.unprotected.Default=%servletContext%/exampleAction
   org.owasp.csrfguard.unprotected.Default_1=%servletContext%/exampleAction
   org.owasp.csrfguard.unprotected.Example=%servletContext%/exampleAction/*
   org.owasp.csrfguard.unprotected.ExampleRegEx=^%servletContext%/.*Public\.do$

5. Change the following configuration properties, to further enhance security. You may need justifiable application level requirements to change them since they will affect performance or user experience.

   Property	Description
   org.owasp.csrfguard.PRNG=SHA1PRNG	Defines the hashing algorithm used to generate the CSRF token.
   org.owasp.csrfguard.TokenLength=32	Defines the length of the CSRF token.
   org.owasp.csrfguard.action.Invalidate=org.owasp.csrfguard.action.Invalidate	Invalidates the user session, if a CSRF attack attempt was blocked by CSRFGuard.