How to list a poster on my CV?
First, I would distinguish between paper presentations and poster presentations in your CV in general, if you don't do this already.

I suggest you list it as you normally would under "Poster Presentations". As long as you make sure that the other coauthors are listed appropriately, there is no reason why this would be an issue. 

Unless you are the first author (which I assume you aren't), most people would probably assume that you're not the presenter, though this isn't too crucial. If you really want, you can specify who was the presenting author, but I think this is probably unnecessary in this case.