The PostmarkApp Email Integrator plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the plugin settings in versions up to, and including, 2.4. This is due to insufficient input sanitization and output escaping on the pma_api_key and pma_sender_address parameters. This makes it possible for authenticated attackers, with Administrator-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses the settings page.