Currently when a WordPress plugin is reported to have a security vulnerability it is removed from the WordPress.org Plugin Directory until the vulnerability has been resolved, but no warning is provided to anyone who already installed it. While many plugins are promptly fixed, there are quite a few that remain vulnerable for a long time or are never fixed. We think that WordPress should alert on the Installed Plugins page in WordPress if an installed plugin has been removed from the directory and provide at least a general reason it has been removed, as many are removed for reasons other than security vulnerabilities, so that appropriate action can be taken by admins. If you would also like to see that happen you can help by voting for our idea on the Ideas section of WordPress.org. To vote you will first need to create a WordPress.org Forum account (or log in if you already have account) and then you can rate the idea by clicking on one of the stars under the heading Rate This (click the right most star for the highest rating for the idea). You can also add your own comments on how the issue should be handled.
Until an alert is added in WordPress itself, you can get a more limited version of this functionality using our No Longer in Directory plugin (we just released our beginning of the month update for the plugin).
While we are discussing the issue of plugin vulnerabilities, we should say that since our last post about this we have been seeing that plugins with Secunia advisories for outstanding issues are being promptly removed from the Plugin Directory until those are resolved. This is great improvement from earlier this year when we found that vulnerable plugins had remained in the directory for years. With that happening we are now looking to make sure that they maintainers of the Plugin Directory are aware of any vulnerabilities which haven’t received Secunia advisories. We just reported a plugin that was found to have a fairly serious information disclosure vulnerability to them and they promptly took action (we alerted the developer of the plugin a week ago and had not received any response). For anyone that finds a vulnerability in a plugin available in the Plugin Directory and is unable to get a response from the developer, you can find directions for contacting the Plugin Directory here.