In Semplice we add SVG images to the allowed filetypes per default. The Problem is that if your SVG file is missing some important parts it can't be uploaded to WordPress.
The missing part if you get an security error is this line:
<?xml version="1.0" encoding="utf-8"?>
To add this line simply open your SVG file in a text editor of your choice and add a new line on the very top of the code and copy+paste the line from above. (it needs to be the first line of the document and make sure to copy the right quotes)
After you saved your file the upload should work fine. :)