I just want a forum software that's as static, lightweight and barebones as phpBB2 but without the security holes because of its obsolescence

PunBB maybe? But I think phpBB2 is OK as long as you remember to keep it up-to-date. Else maybe something Python based like FlaskBB?
Sign in to participate in the conversation
Octodon

Octodon is a nice general purpose instance. more