The Newsletter, SMTP, Email marketing and Subscribe forms by Brevo (formely Sendinblue) plugin for WordPress is vulnerable to Cross-Site Request Forgery in all versions up to, and including, 3.1.87. This is due to missing or incorrect nonce validation on the Init() function. This makes it possible for unauthenticated attackers to log out of a Brevo connection via a forged request granted they can trick a site administrator into performing an action such as clicking on a link.
CWE-352, CWE-352