ntopng: scan port parameter lets authenticated users run OS commands

ntopng is a web-based network traffic monitoring application. Prior to 6.7.260717, scripts/lua/rest/v2/add/host/to_scan.lua and scripts/lua/rest/v2/exec/host/schedule_vulnerability_scan.lua accept scan_ports from any authenticated session, including non-administrator users, while deployments with login disabled expose the same request without authentication. The endpoints validate scan_ports with validateSingleWord, which permits shell metacharacters, and persist the value for the minute vulnerability-scan scheduler. The scheduler concatenates the value into an nmap command through nmap_scan_host and executes it through ntop.execCmd or ntop.execCmdAsync using popen. For the tcp_portscan and cve modules, a preliminary nmap -sn probe must first report the target as up before the attacker-controlled ports are used. When nmap is installed, this command injection allows arbitrary operating-system commands to execute as the ntopng service account without further user interaction. This issue is fixed in version 6.7.260717.