Post SMTP <= 3.4.1 - Missing Authorization to Authenticated (Subscriber+) Limited Plugin Option Update

The Post SMTP – WP SMTP Plugin with Email Logs and Mobile App for Failure Notifications – Gmail SMTP, Office 365, Brevo, Mailgun, Amazon SES and more plugin for WordPress is vulnerable to unauthorized modification of data due to a missing capability check on the 'update_post_smtp_pro_option_callback' function in all versions up to, and including, 3.4.1. This makes it possible for authenticated attackers, with Subscriber-level access and above, to enable pro extensions.