Rust Spotting on 2004 4Runner Rear

Hi, friends. I recently purchased a 2004 4Runner and am looking to address some exterior cosmetic issues. I haven't ever seen a rust pattern like this, especially with the bubbles—granted, I don't have a lot of previous experience with rust, but this looks unusual to me anyway.

Thoughts on how to address this?

 

Looks like rail dust that went unchecked. Need to sand it bare on each spot, prime and touch up paint to stop it.