19. Architecture

19.1. Protocols

There are mandatory and optional protocols. Some protocols are only used in specific setups.

The GSM requires several protocols to fully function. These protocols provide the feed updates, Domain Name System (DNS) resolution, time, etc.

19.1.1. GSM as a Client

_images/gos_acting_as_client_2000x1125.png

Fig. 19.1 GSM acting as a client

The following protocols are used by a standalone system or a GSM master to initiate connections as a client:

DNS – Name resolution

  • Connecting to 53/udp and 53/tcp
  • Mandatory
  • Not encrypted
  • May use internal DNS server

NTP – Time synchronization

  • Connecting to 123/udp
  • Mandatory
  • Not encrypted
  • May use internal NTP server

Feeds (see below)

  • Direct
    • Connecting to 24/tcp or 443/tcp
    • Direct internet access required
  • Via proxy
    • Connecting to internal HTTP proxy supporting CONNECT method on configurable port
  • Connecting to apt.greenbone.net and feed.greenbone.net
  • Mandatory on stand-alone and master appliances
  • Used protocol is SSH
  • Encrypted and bidirectionally authenticated via SSH
    • Server: public key
    • Client: public key

DHCP

  • Connecting to 67/udp and 68/udp
  • Optional
  • Not encrypted

LDAPS – User authentication

  • Connecting to 636/tcp
  • Optional
  • Encrypted and authenticated via SSL/TLS
    • Server: certificate
    • Client: user name/password

Syslog – Remote logging and alerts

  • Connecting to 512/udp or 512/tcp
  • Optional
  • Not encrypted

SNMP traps for alerts

  • Connecting to 162/udp
  • Optional
  • Only SNMPv1
  • Not encrypted

SMTP for e-mail alerts

  • Connecting to 25/tcp
  • Optional
  • Not encrypted

SSH for backup

  • Connecting to 22/tcp
  • Optional
  • Encrypted and bidirectionally authenticated via SSH
    • Server: public key
    • Client: public key

Cisco Firepower (Sourcefire) for IPS integration

  • Connecting to 8307/tcp
  • Optional
  • Encrypted and bidirectionally authenticated via SSL/TLS
    • Server: certificate
    • Client: certificate

verinice.PRO

  • Connecting to 443/tcp
  • Optional
  • Encrypted via SSL/TLS
    • Server: optional via certificate
    • Client: user name/password

TippingPoint SMS

  • Connecting to 443/tcp
  • Optional
  • Encrypted via SSL/TLS
    • Server: certificate
    • Client: certificate, user name/password

19.1.2. GSM as a Server

_images/gos_acting_as_server_2000x1125.png

Fig. 19.2 GSM acting as a server

The following connections are supported by a GSM acting as a server:

HTTPS – Web interface

  • 443/tcp
  • Mandatory on stand-alone and master appliances
  • Encrypted and authenticated via SSL/TLS
    • Server: optional via certificate
    • Client: user name/password

SSH – CLI access and GMP

  • 22/tcp
  • Optional
  • Encrypted and authenticated via SSH
    • Server: public key
    • Client: user name/password

SNMP

  • 161/udp
  • Optional
  • Optionally encrypted when using SNMPv3

19.1.3. Master-Sensor Setup

_images/gos_master_sensor_comm_2000x1125.png

Fig. 19.3 GSM master and sensor

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 and GMP

  • 22/tcp
  • Mandatory
  • Encrypted and bidirectionally authenticated via SSH
    • Server: public key
    • Client: public key

19.2. Security Gateway Considerations

Many enterprises deploy security gateways to restrict the internet access. These security gateways can 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 may even try to decrypt and analyze any encrypted communication.

19.2.1. Standalone/Master GSM

While many protocols used by the GSM are only used internally, some protocols require access to the internet. These protocols may be filtered by such a security gateway.

When deploying the GSM as a standalone appliance or as a master, the GSM needs to be able to access the Greenbone Security Feed. The Greenbone Security Feed can be access directly via port 24/tcp or 443/tcp or using a proxy.

Note

In all cases the used protocol is SSH, even when using the port 443/tcp or a HTTP proxy.

A deep inspection firewall may detect the usage of the SSH protocol running on port 443/tcp and drop or block the traffic.

If the security gateway tries to decrypt the traffic using man-in-the-middle techniques, the communication of the GSM and the feed server fails. The SSH protocol using bidirectional authentication based on public keys prevents any man-in-the-middle approaches by terminating the communication.

Additional protocols which need internet access are DNS and NTP. Both DNS and NTP can be configured to use internal DNS and NTP servers.

19.2.2. Sensor GSM

If security gateways are deployed between the master and the sensor, the security gateway must permit SSH (22/tcp) connections from the master to the sensor.