I want to throw together a site in PHP/mySQL that has some standard user functionality like registration, session management, and ability to leave comments (which can include uploading a picture, if that matters). Not very much beyond that.

From what I read, even the simplest task involving users and security can open up a can of worms, and often a Content Management System is recommended since the code is presumably more robust and secure.

Any thoughts on this? I've never worked with a CMS so it's hard to spot their applications.

Thanks in advance.