I've sold real estate since 2003 and I've seen many rusted railings that needed not just a repair, but a complete replacement. This is such an easy maintenance issue for a property, but you have to catch it before it's too late. This particular railing is on the rear landing of my home. I cleaned the rust off completely with a wire brush and then painted it with an exterior gloss paint (Rustoleum). Looks new again and I'm glad I caught it in time to prevent replacing the entire railing.
Most inspectors and appraisers (especially for FHA and VA loans) will ask that a loose railing be repaired or replaced to prevent injuries, so now's the time to address it if yours looks like the one above.
In case this blog post is too late for you, here's a contractor in MD that is highly recommended for railing repair/replacement: https://www.ironrailingrepair.com/. So, go check those railing posts as soon as you can. You don't need any more headaches as a property owner!