payment_manage.ajax.php and various *_manage.ajax.php in MFScripts YetiShare 3.5.2 through 4.5.4 directly insert values from the sSortDir_0 parameter into a SQL string. This allows an attacker to inject their own SQL and manipulate the query, typically extracting data from the database, aka SQL Injection. NOTE: this issue exists because of an incomplete fix for CVE-2019-19732.
MFScripts YetiShare v3.5.2 through v4.5.4 places sensitive information in the Referer header. If this leaks, then third parties may discover password-reset hashes, file-delete links, or other sensitive information.
The user-introduction email in MFScripts YetiShare v3.5.2 through v4.5.4 may leak the (system-picked) password if this email is sent in cleartext. In other words, the user is not allowed to choose their own initial password.