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Nexus Hybrid Access Gateway is shipped as a virtual appliance that uses an Ubuntu base image. With every release of Hybrid Access Gateway this base image is hardened in different areas:

  • Only installing required software and services
  • Restricted user management
  • Continuous security updates 

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 Installed services

During the installation, Hybrid Access Gateway installs the OpenSSH server for communication from outside. A Postgres database is installed and only used for local communication. Connections from outside are disabled by default.

During the installation, the default firewall of Ubuntu is applied. Only features that comes by default with the corresponding Ubuntu base image (currently 18.04) are available within the Hybrid Access Gateway appliance, including:

  • Simple Network Management Protocol (SNMP)
    SNMP is configured to send information related to its services and system health. However, by default it does not send information to any location as it does not know who the recipient would be. For this, the customer needs to un-comment the trapsess command in the file /etc/snmp/snmpd.conf and point it to their SNMP manager to start sending information.
  • Network Time Protocol (NTP)
    NTP is installed and set to as default. You can change the value over the VM wizard.

If Hybrid Access Gateway is configured to use an external database for users, reporting and OATH, the internal Postgres database service can be turned off without any hassle.


To improve the hardening index of Hybrid Access Gateway, an SSH configuration parameter (MaxAuthTries) was introduced with Hybrid Access Gateway version 5.13.0. This configuration parameter limits the maximal authentication attempts to the amount of two. This change can affect the SSH authentication, if the client has more than one private key configured that is not configured for the corresponding user in Hybrid Access Gateway. In this case, an authentication with username and password will fail. If this setting affects you, you can increase the amount of authentication attempts.

To increase the amount of authentication attempts:

  1. Change the parameter
    MaxAuthTries within the file /etc/ssh/sshd_config to a suitable number.

In case of Hybrid Access Gateway upgrades, this change has to be done after the appliance has been upgraded successfully.

 Restricted user management

All services in Hybrid Access Gateway are run by a separate user named pwuser. Authentication from outside is not allowed with that user. For authentication from outside, the user agadmin is created during installation.

Writing permissions to Hybrid Access Gateway-related files are restricted to power users, such as pwuser and root.

Because of security reasons, the passwords of pwuser and root can be changed after installation. To do this, use sudo access of agadmin or root. The pwuser could still not be used to authenticate from outside after this change. All passwords are saved as part of the default location of passwords. 

Change root password

  1. To change the root password:
    1. Type the following command to become root user and issue passwd
      sudo -i passwd
    2. or set a password for root user in a single command
      sudo passwd root
 Continuous security updates

With every release of Hybrid Access Gateway, all binaries are updated to the latest versions to prevent security vulnerabilities as much as possible. Therefore, vulnerabilities like Spectre and Meltdown are taken care off as soon as updates are available. A steady release cycle ensures prompt security updates.

 Secure communication

The communication between Hybrid Access Gateway nodes is secured with a Nexus proprietary protocol called LCP. The protocol is based on length, type and value. LCP uses a shared secret which is initialized during the system setup. Once the secret is shared among all the registered nodes the secret is never shared again. Although, it is possible to update the secret time-to-time for security purpose. To update the secret, use one of the two following methods:

  • Setting the secret manually into each node.


  • Distribution via the Hybrid Access Gateway administration interface for particular nodes. The secret will be sent to the nodes using LCP protocol, protected with the previous secret.

The following types of data are encrypted over LCP:

  • Shared key hash in Server/Client Hello
  • SSO credentials
  • Authentication credentials
  • Encryption key used when importing a PSKC file
 Penetration testing

On a regular basis, Nexus instructs specialized, external companies to perform penetration tests on the latest versions of Hybrid Access Gateway, to ensure that it maintains it high security status.

Critical vulnerabilities found by PEN testing will be fixed as soon as possible and released with the next version (or an interim version if required).

This article is valid from Hybrid Access Gateway 5.13.1.

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