CSRF Lab-02
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Cross-Site Request Forgery (CSRF) Attack Lab (Web Application: Elgg)
1 Overview
The objective of this lab is to help students understand the Cross-Site Request Forgery (CSRF) attack. A CSRF attack involves a victim user, a trusted site, and a malicious site. The victim user holds an active session with a trusted site while visiting a malicious site. The malicious site injects an HTTP request for the trusted site into the victim user session, causing damages.
In this lab, students will be attacking a social networking web application using the CSRF attack. The open-source social networking application is called Elgg, which has already been installed in our VM. Elgg has countermeasures against CSRF, but we have turned them off for the purpose of this lab. This lab covers the following topics:
• Cross-Site Request Forgery attack
• CSRF countermeasures: Secret token and Same-site cookie • HTTP GET and POST requests
• JavaScript and Ajax
Permission on Attacker folder
The Elgg web application is in the var/www/csrf. You will find Attacker folder there. If you see a lock symbol on the Attacker folder, it means that you don’t have permission to save any scripts here. This is the folder where attacker web scripts will be stored. We need to change permission on it.
In the terminal
seed@VM:~$ cd /var/www/CSRF/ seed@VM:…/CSRF$ sudo chown seed Attacker seed@VM…/CSRF$ cd Attacker seed@VM:…/Attacker$ gedit index.html
Note:
// make seed user owner on the Attacker folder //change into Attacker folder
// check if you are able to save a file in the Attacker folder You may need to assign full permission chmod 777 on the Attacker folder if chown did not work.
2 Lab Environment
This lab can only be conducted in our Ubuntu 16.04 VM, because of the configurations that we have performed to support this lab. We summarize these configurations in this section.
The Elgg Web Application. We use an open-source web application called Elgg in this lab. Elgg is a web- based social-networking application. It is already set up in the pre-built Ubuntu VM image. We have also created several user accounts on the Elgg server and the credentials are given below.

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User
UserName
Password
Admin Alice Boby Charlie Samy
admin alice boby charlie samy
seedelgg seedalice seedboby seedcharlie seedsamy
DNS Configuration.
This lab involves two websites, the victim website and the attacker’s website. Both websites are set up on our VM. Their URLs and folders are described in the following:
The above URLs are only accessible from inside the virtual machine, because we have modified the /etc/hosts file to map the domain name of each URL to the virtual machine’s local IP address (127.0.0.1). You may map any domain name to a particular IP address using /etc/hosts. For example, you can map http://www.example.com to the local IP address by appending the following entry to /etc/hosts:
127.0.0.1 www.example.com
If your web server and browser are running on two different machines, you need to modify /etc/hosts on the browser’s machine accordingly to map these domain names to the web server’s IP address, not to 127.0.0.1.
Apache Configuration.
In our pre-built VM image, we used Apache server to host all the web sites used in the lab. The name- based virtual hosting feature in Apache could be used to host several web sites (or URLs) on the same machine. A configuration file named 000-default.conf in the directory “/etc/ apache2/sites-available” contains the necessary directives for the configuration:
Inside the configuration file, each web site has a VirtualHost block that specifies the URL for the web site and directory in the file system that contains the sources for the web site. The following examples show how to configure a website with URL http://www.example1.com and another website with URL http://www.example2.com:
Attacker’s website
URL: http://www.csrflabattacker.com Folder: /var/www/CSRF/Attacker/
Victim website (Elgg)
URL: http://www.csrflabelgg.com Folder: /var/www/CSRF/Elgg/

ServerName http://www.example1.com DocumentRoot /var/www/Example_1/


ServerName http://www.example2.com DocumentRoot /var/www/Example_2/

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You may modify the web application by accessing the source in the mentioned directories. For example, with the above configuration, the web application http://www.example1.com can be changed by modifying the sources in the /var/www/Example_1/ directory. After a change is made to the configuration, the Apache server needs to be restarted. See the following command:
$ sudo service apache2 start
3 Lab Tasks
For the lab tasks, you will use two web sites that are locally setup in the virtual machine. The first web site is the vulnerable Elgg site accessible at www.csrflabelgg.com inside the virtual machine. The second web site is the attacker’s malicious web site that is used for attacking Elgg. This web site is accessible via www.csrflabattacker.com inside the virtual machine.
Solutions for this lab: Attack on Get and Post request were demonstrated in the lecture delivered on Friday 20th of Nov. You should be able to see steps there. The two attack scripts are provided in Canvas. You should attempt yourself first.
3.1 Task 1: Observing HTTP Request.
You should have completed this task last week. If not can you make sure that you are familiar with HTTP Header Live tool. You will need to install it on FireFox from addon. See guidelines in this lab in section 4, if you have not done this task last week.
In Cross-Site Request Forget attacks, we need to forge HTTP requests. Therefore, we need to know what a legitimate HTTP request looks like and what parameters it uses, etc. We can use a Firefox add-on called “HTTP Header Live” for this purpose. The goal of this task is to get familiar with this tool.
3.2 Task 2: CSRF Attack using GET Request
In this task, we need two people in the Elgg social network: Alice and Boby. Boby wants to become a friend to Alice, but Alice refuses to add him to her Elgg friend list. Boby decides to use the CSRF attack to achieve his goal. He sends Alice an URL (via an email or a posting in Elgg); Alice, curious about it, clicks on the URL, which leads her to Boby’s web site: www.csrflabattacker.com. Pretend that you are Boby, describe how you can construct the content of the web page, so as soon as Alice visits the web page, Boby is added to the friend list of Alice (assuming Alice has an active session with Elgg).
To add a friend to the victim, we need to identify what the legitimate Add-Friend HTTP request (a GET request) looks like. We can use the “HTTP Header Live” Tool to do the investigation. In this task, you are not allowed to write JavaScript code to launch the CSRF attack. Your job is to make the attack successful as soon as Alice visits the web page, without even making any click on the page (hint: you can use the img tag, which automatically triggers an HTTP GET request).
Elgg has implemented a countermeasure to defend against CSRF attacks. In Add-Friend HTTP requests, you may notice that each request includes two wired-looking parameters, elggts and elggtoken. These parameters are used by the countermeasure, so if they do not contain correct values, the request will not be accepted by Elgg. We have disabled the countermeasure for this lab, so there is no need to include these two parameters in the forged requests.

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3.3 Task 3: CSRF Attack using POST Request
After adding himself to Alice’s friend list, Boby wants to do something more. He wants Alice to say “Boby is my Hero” in her profile, so everybody knows about that. Alice does not like Boby, let alone putting that statement in her profile. Boby plans to use a CSRF attack to achieve that goal. That is the purpose of this task.
One way to do the attack is to post a message to Alice’s Elgg account, hoping that Alice will click the URL inside the message. This URL will lead Alice to your (i.e., Boby’s) malicious web site www. csrflabattacker.com, where you can launch the CSRF attack.
The objective of your attack is to modify the victim’s profile. In particular, the attacker needs to forge a request to modify the profile information of the victim user of Elgg. Allowing users to modify their profiles is a feature of Elgg. If users want to modify their profiles, they go to the profile page of Elgg, fill out a form, and then submit the form—sending a POST request—to the server-side script /profile/edit.php, which processes the request and does the profile modification.
The server-side script edit.php accepts both GET and POST requests, so you can use the same trick as that in Task 1 to achieve the attack. However, in this task, you are required to use the POST request. Namely, attackers (you) need to forge an HTTP POST request from the victim’s browser, when the victim is visiting their malicious site. Attackers need to know the structure of such a request. You can observe the structure of the request, i.e., the parameters of the request, by making some modifications to the profile and monitoring the request using the “HTTP Header Live” tool. You may see something similar to the following. Unlike HTTP GET requests, which append parameters to the URL strings, the parameters of HTTP POST requests are included in the HTTP message body (see the contents between the two P symbols):
http://www.csrflabelgg.com/action/profile/edit
POST /action/profile/edit HTTP/1.1
Host: www.csrflabelgg.com User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux i686; rv:23.0) … Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: http://www.csrflabelgg.com/profile/elgguser1/edit
Cookie: Elgg=p0dci8baqrl4i2ipv2mio3po05
Connection: keep-alive
Content-Type: application/x-www-form-urlencoded
Content-Length: 642 __elgg_token=fc98784a9fbd02b68682bbb0e75b428b&__elgg_ts=1403464813 P &name=elgguser1&description=%3Cp%3Iamelgguser1%3C%2Fp%3E &accesslevel%5Bdescription%5D=2&briefdescription= Iamelgguser1 &accesslevel%5Bbriefdescription%5D=2&location=US
…… P
After understanding the structure of the request, you need to be able to generate the request from your attacking web page using JavaScript code. To help you write such a JavaScript program, we provide a sample code in the following You can use this sample code to construct your malicious web site for the CSRF attacks. This is only a sample code, and you need to modify it to make it work for your attack.

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This page forges an HTTP POST request.

In Line À, the value 2 sets the access level of a field to public. This is needed, otherwise, the access level will be set by default to private, so others cannot see this field. It should be noted that when copy- and pasting the above code from a PDF file, the single quote character in the program may become something else (but still looks like a single quote). That will cause syntax errors. Replace all the single quote symbols with the one typed from your keyboard will fix those errors.

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3.4 Task 4: Implementing a countermeasure for Elgg
Elgg does have a built-in countermeasures to defend against the CSRF attack. We have commented out the countermeasures to make the attack work. CSRF is not difficult to defend against, and there are several common approaches:
• Secret-token approach: Web applications can embed a secret token in their pages, and all requests coming from these pages will carry this token. Because cross-site requests cannot obtain this token, their forged requests will be easily identified by the server.
• Referrer header approach: Web applications can also verify the origin page of the request using the referrer header. However, due to privacy concerns, this header information may have already been filtered out at the client side.
The web application Elgg uses secret-token approach. It embeds two parameters elggts and elggtoken in the request as a countermeasure to CSRF attack. The two parameters are added to the HTTP message body for the POST requests and to the URL string for the HTTP GET requests.
Elgg secret-token and timestamp in the body of the request. Elgg adds security token and timestamp to all the user actions to be performed. The following HTML code is present in all the forms where user action is required. This code adds two new hidden parameters elggts and elggtoken to the POST request:
The elggts and elgg token are generated by the views/default/input/securitytoken.
php module and added to the web page. The code snippet below shows how it is dynamically added to the web page.
Elgg also adds the security tokens and timestamp to the JavaScript which can be accessed by
elgg.security.token.__elgg_ts; elgg.security.token.__elgg_token;
Elgg security token is a hash value (md5 message digest) of the site secret value (retrieved from database), timestamp, user sessionID and random generated session string. There by defending against the CSRF attack. The code below shows the secret token generation in Elgg.

$ts = time(); $token = generate_action_token($ts);
echo elgg_view(’input/hidden’, array(’name’ => ’__elgg_token’, ’value’ =>
$token)); echo elgg_view(’input/hidden’, array(’name’ => ’__elgg_ts’, ’value’ => $ts));

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function generate_action_token($timestamp) {
$site_secret = get_site_secret(); $session_id = session_id();
// Session token
$st = $_SESSION[’__elgg_session’];
if (($site_secret) && ($session_id))
{ return md5($site_secret . $timestamp . $session_id . $st); }
return FALSE; }
The PHP function sessionid() is used to get or set the session id for the current session. The below code snippet shows random generated string for a given session elggsession apart from public user Session ID.
Elgg secret-token validation. The elgg web application validates the generated token and timestamp to defend against the CSRF attack. Every user action calls validateactiontoken function and this function validates the tokens. If tokens are not present or invalid, the action will be denied and the user will be redirected.
The below code snippet shows the function validateactiontoken.
……
// Generate a simple token (private from potentially public session id) if (!isset($_SESSION[’__elgg_session’])) {
$_SESSION[’__elgg_session’] =
ElggCrypto::getRandomString(32,ElggCrypto::CHARS_HEX); ……..

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function validate_action_token($visibleerrors = TRUE, $token = NULL, $ts = NULL) { if (!$token) { $token = get_input(’__elgg_token’); } if (!$ts) {$ts =
get_input(’__elgg_ts’); }
$session_id = session_id(); if (($token) && ($ts) && ($session_id)) {
// generate token, check with input and forward if invalid $required_token = generate_action_token($ts);
// Validate token if ($token == $required_token) {
if (_elgg_validate_token_timestamp($ts)) {
// We have already got this far, so unless anything
// else says something to the contrary we assume we’re ok $returnval = true; ……
} else { …… register_error(elgg_echo(’actiongatekeeper:tokeninvalid’)); ……
} …… }
Turn on countermeasure.
To turn on the countermeasure, please go to the directory /var/www/CSRF/ Elgg/vendor/elgg/elgg/engine/classes/Elgg and find the function gatekeeper in the ActionsService.php file. In function gatekeeper() please comment out the “return true;” statement as specified in the code comments.
Task: After turning on the countermeasure above, try the CSRF attack again, and describe your observation.
Note why the attacker cannot send these secret tokens in the CSRF attack; what prevents them from finding out the secret tokens from the web page?
public function gatekeeper($action) { //SEED:Modified to enable CSRF.
//Comment the below return true statement to enable countermeasure return true; ……
}

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3B – Useful external tutorials – take idea for your coursework from the following
The links listed below are useful to take simple idea for your coursework about how to generate and implement secret token. You will be using your XAMPP environment that you set up in labs 3-6 to practice and implement these examples.
1)
https://riptutorial.com/php/example/19314/cross-site-request-forgery#undefined
2

Guidelines
Using the “HTTP Header Live” add-on to Inspect HTTP Headers
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4.1
The version of Firefox (version 60) in our Ubuntu 16.04 VM does not support the LiveHTTPHeader add-on, which was used in our Ubuntu 12.04 VM. A new add-on called “HTTP Header Live” is used in its place. The instruction on how to enable and use this add-on tool is depicted in Figure 1. Just click the icon marked by À; a sidebar will show up on the left. Make sure that HTTP Header Live is selected at position Á. Then click any link inside a web page, all the triggered HTTP requests will be captured and displayed inside the sidebar area marked by Â. If you click on any HTTP request, a pop-up window will show up to display the selected HTTP request. Unfortunately, there is a bug in this add-on tool (it is still under development); nothing will show up inside the pop-up window unless you change its size (It seems that re-drawing is not automatically triggered when the window pops up, but changing its size will trigger the re-drawing).
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Figure 1: Enable the HTTP Header Live Add-on
Following Sections are optional but highly recommended for those who want to have a career in web security.
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1

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DVWA – Damn Vulnerable Web Application (Very famous for web security)
If you want to have a career in security especially web security then you should be
exploring and practicing with more hands on vulnerable application like DAMN. a) Install it from here http://www.dvwa.co.uk/
b) Host it in your Apache virtual hosts
c) Knowledge gained in this lab, can be applied to it.
4. 2 Using the Web Developer Tool to Inspect HTTP Headers
There is another tool provided by Firefox that can be quite useful in inspecting HTTP headers. The tool is the Web Developer Network Tool. In this section, we cover some of the important features of the tool. The Web Developer Network Tool can be enabled via the following navigation:
We use the user login page in Elgg as an example. Figure 2 shows the Network Tool showing the HTTP POST request that was used for login.
Figure 2: HTTP Request in Web Developer Network Tool
To further see the details of the request, we can click on a particular HTTP request and the tool will show the information in two panes (see Figure 3).
Figure 3: HTTP Request and Request Details in Two Panes
Click Firefox’s top right menu –> Web Developer –> Network or Click the “Tools” menu –> Web Developer –> Network

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The details of the selected request will be visible in the right pane. Figure 4(a) shows the details of the login request in the Headers tab (details include URL, request method, and cookie). One can observe both request and response headers in the right pane. To check the parameters involved in an HTTP request, we can use the Params tab. Figure 4(b) shows the parameter sent in the login request to Elgg, including username and password. The tool can be used to inspect HTTP GET requests in a similar manner to HTTP POST requests.
Font Size. The default font size of Web Developer Tools window is quite small. It can be increased by focusing click anywhere in the Network Tool window, and then using Ctrl and + button.
4.3 JavaScript Debugging
We may also need to debug our JavaScript code. Firefox’s Developer Tool can also help debug JavaScript code. It can point us to the precise places where errors occur. The following instruction shows how to enable this debugging tool:
Once we are in the web console, click the JS tab. Click the downward pointing arrowhead beside JS and ensure there is a check mark beside Error. If you are also interested in Warning messages, click Warning. See Figure 5.
If there are any errors in the code, a message will display in the console. The line that caused the error appears on the right side of the error message in the console. Click on the line number and you will be taken
(a) HTTP Request Headers (b) HTTP Request Parameters Figure 4: HTTP Headers and Parameters
Click the “Tools” menu –> Web Developer –> Web Console or use the Shift+Ctrl+K shortcut.

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Figure 5: Debugging JavaScript Code (1) to the exact place that has the error. See Figure 6.
Acknowledgement.
Figure 6: Debugging JavaScript Code (2)
Copyright © 2006 – 2016 Wenliang Du, All rights reserved.
Free to use for non-commercial educational purposes. Commercial uses of the materials are prohibited. The SEED project was funded by multiple grants from the US National Science Foundation.