Premium SEO - Unauthenticated Backdoor (Admin Creation / RCE / SSRF / Content Injection)

The Premium SEO WordPress plugin is malicious: it ships an unauthenticated backdoor that creates a hidden administrator account and, in some builds, also enables remote code execution, server-side request forgery and arbitrary front-end script/content injection, giving an unauthenticated attacker full control of the affected site.