This chapter covers the architecture and the communication protocols used by the Greenbone Security Manager. Some protocols are mandatory and some protocols are optional. Some protocols are only used in specific setups.
The GSM requires several protocols to fully function. These protocols provide the feed updates, DNS resolution, time, etc. The following protocols are used by a stand alone system or a GSM master to initiate connections being a client:
The following connection are accepted by a GSM acting as a server.
In a master/sensor setup the following additional requirements apply. The master (client) initiates two additional connections to the sensor (server):
SSH for Updates and Feeds
encrypted and bidirectionally authenticated via SSH
- Server: public key
- Client: public key
OMP for scan control
Many enterprises deploy security gateways to restrict the Internet access. These security gateways may operate as packet filters or application layer gateways. Some products support deep inspection and try to determine the actual protocol used in the communication channels. They might even try to decrypt and analyze any encrypted communication.
While many protocols used by the GSM are only used internally, some protocols require access to the Internet. These might be filtered by such a security gateway. When deploying the GSM as standalone appliance or master the GSM needs to be able to access the Greenbone security feed. The Greenbone security feed may be access directly via port 24/tcp or 443/tcp or using a proxy. In all cases the actual protocol used is SSH. Even when using the port 443/tcp or a HTTP proxy the protocol used is SSH.
A deep inspection firewall might detect the usage of the SSH protocol running on port 443/tcp and could drop or block the traffic. If the security gateway would try to decrypt the traffic using man-in-the-middle techniques the communication of the GSM and the Feed server will fail. The SSH protocol using bidirectional authentication based on public keys will prevent any man-in-the-middle approach by terminating the communication.
Additional protocols which might need Internet access are DNS and NTP. Both DNS and NTP may be configured to use internal DNS and NTP servers.
If security gateways are deployed between the master and the sensor the security gateway must permit SSH (22/tcp) and OMP (9390/tcp) connections from the master to the sensor.