For plugins, a quick search in the WordPress plugins directly lists several of them:
https://www.ads-software.com/plugins/search/forum/
Popular ones include Simple:Press, WPForo, bbPress, Asgaros Forum, etc… plus a bunch of Q&A-style forum plugins.
My main concern is the security side of things.
Security is not like an on/off switch (secure/not-secure). It’s more like a dial, with numerous stops along the way. It’s also not a single dial… but numerous dials. And the plugin’s codebase is just ONE single stop point on ONE of these dials.
What are you concerned about as far as security is concerned?
Building a successful forum is a major undertaking, and you really need to spend time to identify what features are important to your users, what you need to administer and grow your forum, what aspects of security (with codebase being just one of them) are critical for you to nail down… and research which plugins meet your requirements.
Just picking a random “recommendation” from someone who has no knowledge of your use-case and requirements is a recipe for disaster down the road.
