Network Manager VPNC Username Privilege Escalation

This module exploits an injection vulnerability in the Network Manager
VPNC plugin to gain root privileges.

This module uses a new line injection vulnerability in the configured
username for a VPN network connection to inject a `Password helper`
configuration directive into the connection configuration.

The specified helper is executed by Network Manager as root when the
connection is started.

Network Manager VPNC versions prior to 1.2.6 are vulnerable.

This module has been tested successfully with VPNC versions:
1.2.4-4 on Debian 9.0.0 (x64); and
1.1.93-1 on Ubuntu Linux 16.04.4 (x64).