The Theme My Login plugin for WordPress is vulnerable to Missing Authorization in versions up to, and including, 7.1.15 on Multisite installations

Overview

The Theme My Login plugin for WordPress is vulnerable to Missing Authorization in versions up to, and including, 7.1.15 on Multisite installations. This is due to the tml_ms_signup_handler() function's gimmeanotherblog branch failing to enforce the network's active_signup registration policy, checking only is_user_logged_in() while sibling branches such as validate-blog-signup apply the full policy gate. This makes it possible for authenticated attackers, with Subscriber-level access and above, to directly POST stage=gimmeanotherblog to Theme My Login's signup route, bypassing the configured registration policy entirely — even when it is set to none or user — which causes wpmu_create_blog() to execute with the attacker's user ID, after which WordPress core assigns the Administrator role on the newly created subsite via add_user_to_blog(). The privilege gain is scoped to the newly created subsite only; the attacker's account retains Subscriber-level access on the main site and does not obtain Super Admin or network-level capabilities such as manage_network or manage_sites.

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.