The vulnerability was patched in WordPress v4.7.2 two weeks ago, but millions of sites haven’t yet updated. This leaves them open to a vulnerability in the WordPress REST API, which can allow malicious actors to edit any post on a site.
Ars Technica has a very nice writeup on the effects of the exploit, which has resulted in the defacement of a staggering number of websites (including the websites of Glenn Beck, the Utah Office of Tourism, and even the official Suse Linux site). Sucuri and Wordfence also have very good articles about the effects of the vulnerability.
If you have a WordPress site, you should immediately check to make sure you’re on the latest version (v4.7.2).