The way the fandom currently operates is that cub art is generally kicked under the rug. Yeah, InkBunny is technically the only place where you can specifically get away with it scot-free, but as this thread demonstrates FurAffinity is absolutely willing to look the other way or intentionally not pay attention to these issues by handwaving matters away with boilerplate excuses. Likewise, there does not seem to be any actual rules one way or the other on SoFurry either, as you can straight up plop "cub" into the search bar and bring up all sorts of artwork and stories pertaining to it. Furry Network does not disallow cub art either, however when they were confronted about this their solution was to automatically add the tag "cub" to everyone's default content filter (which the person can then remove at their discretion). They didn't do anything about the art itself. (I am not sure what Weasyl's stance on the matter is as I never used their website, and don't even know if it's still around.)
In regards to convention stuff I believe many conventions try to ban that kind of content, but it gets through anyways under the "ask for forgiveness, not permission" train of thought. Cub artists know full well that if they ask con staff if they can bring their art they're going to be told no, so they do it without asking and when they get caught usually pull some BS "sorry I didn't know it won't happen again" routine.
What really ought to happen these days, and I feel like I'm going to sound crazy for thinking this, is that the fandom really should have it's own universal "sex predator" list. A repository of artists and people who either create or engage in subject matter that is considered morally questionable or offensive, like cub art. As long as it's managed in black and white terms there's no risk of bias, and this database could then be used by conventions and other fandom community efforts to immediately weed out creeps from even registering for the events because they'd be caught right away and denied. I realize this isn't a perfect system though.