WMF/EMF has had an infamous history of security problems—most famously, RCE in 2005: https://en.wikipedia.org/wiki/Windows_Metafile_vulnerability
Surprisingly it is still the only supported vector format in Office...
https://support.office.com/en-us/article/Insert-SVG-images-i...
Only 17 years after the spec was established.
Looks like it's a brand new feature only available since this year and only for Office 365 customers (for now, I hope), given that it's not supported on my Office 2016 build.