I suppose it depends on what you define as a CMS. If you just want user authentication by displaying web pages, then it is entirely possible to do this with a static web server (assuming that it supports authentication mechanisms and SSL).
If you want the material to be searchable, you will need the server side SOMETHING, which performs indexing (the actual search can still be performed on the client side by downloading the corresponding index files). Or click on Google, but this only works if you do not have security requirements.
If you want to upload files, your server must also handle this.
Without specifying exactly what you are looking for, there is no way to answer this question.
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