The Lightbox with PhotoSwipe WordPress plugin before 5.9.0 does not sanitise or escape a link data attribute before rendering it into the image lightbox caption in the browser, allowing users with author-level access and above (who lack the unfiltered_html capability) to store JavaScript that runs when a visitor or administrator opens the lightbox.
https://wpscan.com/vulnerability/aae59cb8-b259-464e-a86b-164d89f61342/