The Pretty Links plugin for WordPress is vulnerable to Stored Cross-Site Scripting via various IP headers as well as the referer header in versions up to, and including, 2.1.9 due to insufficient input sanitization and output escaping in the track_link function. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.
The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.