If logged in as an admin on any site you can go to settings, Relevanssi Premium, import or export options. This is a text field that accepts a serialised PHP object. It is possible to submit a string that contains an evil encoded object that executes arbitrary code (if there are classes available with particular methods such as
Proof of concept
Achieving arbitrary code execution depends on which classes are available (i.e. which plugins and themes are installed and active). It won’t be possible in all situations.
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