Are there any customizable vulnerability notification services?
2020 update: CVE Details has silently stopped being updated.
CVE Details allows you to "generate a custom RSS feed or an embedable vulnerability list widget or a json API call url", filterable on a large range of fields including product.
The Exploit Database have a twitter feed that updates regularly.
You could use tweetalarm with the keyword [webapps] - Wordpress, and set it to email you whenever a tweet containing that keyword is used. Then you would know about verified exploits for WordPress as soon as they are added to the database.
US-CERT provides a free alerting service. They also have feeds from NCAS, which you can sign up for here: https://www.us-cert.gov/mailing-lists-and-feeds
While they don't offer a specific technology or product feed, you could filter them out yourself.