In Webmin through 1.910, any user authorized to the "Package Updates" module can execute arbitrary commands with root privileges via the data parameter to update.cgi.
pfSense before 2.1.4 allows remote authenticated users to execute arbitrary commands via (1) the hostname value to diag_dns.php in a Create Alias action, (2) the smartmonemail value to diag_smart.php, or (3) the database value to status_rrd_graph_img.php.