I am pretty sure this comes from a malicious ad, not necessarily via sovrn though, probably at some other point down the line and more than one SSP could be affected. I am using prebid BTW.
Here are some of the redirected domains:
Here are some screenshots, also with console messages on a cross-site-scripting attempt to redirect to
kankanpian.cc and a list of all documents referring to
I hope these infos are of help.