The Newsletters plugin for WordPress is vulnerable to authorization bypass in all versions up to, and including, 4.17. This is due to the plugin not properly verifying that a user is authorized to perform an action. This makes it possible for authenticated attackers, with author-level access and above, to send arbitrary newsletter emails to users of any WordPress role, including administrators, by forging POST fields during a normal post submission. This allows an attacker-supplied role slug via the newsletters_mailinglistsroles POST field to be passed directly to get_users(), enabling unauthorized mass-mailing and potential phishing against privileged site users through the site's own outbound email channel.
Exploitability
AV:NAC:LPR:LUI:NScope
S:UImpact
C:NI:LA:N4.3/CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:NAccess Control