One of our clients was getting spam comments on her media attachment pages, so I found this handy little plugin to make it so the attachment pages are no longer available for those kinds of shenanigans. It solves the problem nicely by redirecting each page to the media file itself.
A similar feature is available in Yoast SEO, so if you have that plugin, you can go to SEO -> Search Appearance -> Media tab and turn on the option to Redirect attachment URLs. Sweet!