Input validation vulnerability in Email Notification on Login 1.6.1

The Email Notification on Login plugin for WordPress has a security issue that could allow hackers to inject harmful code into certain pages. This can happen on versions 1.6.1 and below because the plugin does not properly clean up user input and output. This vulnerability can only be exploited by attackers who have administrator-level access or higher on multi-site installations or installations where unfiltered_html is disabled.