If you don’t mind disabling pings to all of your older posts to stop this string of trackback spam, read on.
I’m not moderating anymore, because this is the workaround without having to moderate all comments. It requires the ability to log into phpMyAdmin. In your database, run this SQL query.
None of my older posts are getting trackback spam, and pinging is disabled for the meantime. Thanks to O.F. Jay for the help! Regular commenting should be back to normal.