IT guy here. That's pretty fucking bad. Like.... really bad. Especially if it was combined with the solarwinds stuff a bit back. Exchange is emails, and internal email servers. They can basically get into all of the emails with admin level permissions with this exploit and likely already have at a bunch of places. If sysadmins are getting this fixed or contained right now, then they have a problem.

What does this effect? Mostly people/companies that run their own email servers internally. This can essentially open them up like Hillary's closet server.