STORED XSS in █████████/nlc/login.aspx via "edit" GET parameter through markdown editor [HtUS]

How it was found

While looking through the source code of https://████████/nlc/login.aspx,I noticed this line (204): <a id="ctl00_ContentPlaceHolder1_CancelButton" class="hidden" href="login.aspx?edit=false"><i class="fa fa-times"></i> Cancel</a> ,which exposes the edit GET parameter. Upon accessing https://█████████/nlc/login.aspx?edit=true ,a hidden markdown editor will be revealed if you click around where the bottom text is,which allow us to input our own text,upload images,and pretty much anything you can do in markdown.
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As you can see to prove impact,I inputted an XSS payload(svg/onload=alert(1)>) and clicked on Save. After that whenever anyone accesses https://██████████/nlc/login.aspx ,the XSS payload will execute.
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The only way to remove the XSS payload is through accessing the markdown editor through https://█████████/nlc/login.aspx?edit=true ,removing it,and saving it.

Impact

Using this,an attacker is able to input and execute his own javascript code that will execute on everyone that accesses the login page every time,no matter what device they're using.They are not limited to Stored XSS though,using the hidden markdown editor they're able to upload images,deface the website and basically anything you can using markdown,however the most impactful scenario being executing arbitrary javascript code.