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Barracuda CloudGen Firewall

How to Configure SSH

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The SSH daemon listens on all management IP address on TCP port 22. Connect to the firewall with SSH when performing software updates or other special maintenance tasks. You can use both external SSH clients, or connect via the SSH tab in Barracuda Firewall Admin.

You can use an external SSH client to open an SSH connection to the Barracuda CloudGen Firewall. You can also use the terminal integrated in Barracuda Firewall Admin; direct access to the Barracuda CloudGen Firewall is provided via SSH version 2. To access the SSH terminal, click the SSH tab. 

You can enable event notifications for SSH, as well as view the SSH log for information such as system access and remote command execution. In the Select Log File list on the Logs page, you can find the sshd log file in the Box directory.

Use an External SSH Client

If you prefer to use your own SSH client, configure Barracuda Firewall Admin with the path to the executable:

  1. Click on the OPTIONS tab in the top left corner.
  2. Select Settings.
  3. Expand the Client Settings section.
  4. In the External SSH Client enter the command for for external SSH client. use %ip and %user to dynamically insert the IP address and user name. E.g., C:\putty.exe %user@%ip

Configure SSH

  1. Go to CONFIGURATION > Full Configuration > Box > Advanced Configuration > SSH.
  2. Click Lock.
  3. To configure the general settings for SSH, click Basic Setup from the Configuration menu in the left navigation pane.
    Basic Setup Settings

    On the Basic Setup page for SSH, you can configure the following settings in the General Settings section:

    Setting Description
    Event on SSH 

    Specifies if event notifications should be triggered when the system succeeds or fails to start up or shut down (Events Daemon Startup Failed/Succeeded [2070/2071] and Daemon Shutdown Failed/Succeeded [2072/2073]). You can select any of the following options:

    • Startup Failure
    • Startup/Shutdown Failure
    • Startup/Shutdown Failure + Startup Success
    • Startup/Shutdown Failure + Startup/Shutdown Success

    You are not notified when SSHd is killed manually or just dies unexpectedly. These settings only pertain to SSHd behavior during controlled start or stop sequences.

    Allow TCP Forwarding

    Specifies if TCP is enabled or disabled. This setting is only available in Advanced View mode.

     Disabling TCP forwarding does not improve security. You must also deny shell access to users because forwarders can be installed with the ssh command.

    Login Timeout 

    The maximum length of time in seconds that a user has to successfully log in before the server disconnects. The minimum time limit is 10 seconds. The default length of time is 90 seconds. 

    Permit Root Login

     

    Permits or prohibits SSH logins for the root user.

    If you prohibit SSH logins for the root user, the following configuration entities will not work: Box Exec tab and Software Update tab.


    Check User Home

    Specifies whether sshd should check file modes and ownership of the user's files and home directory before accepting login. This is normally desirable because novices sometimes accidentally leave their directories or files writable. The default is yes. This setting is only available in Advanced View mode.

    Send Keepalives 

    Specifies if the server should send keepalive messages. Default: yes.

    • To avoid hanging sessions, enable keepalive messages to monitor the connection. The server notices if the network goes down or the client host reboots. However, this may cause some inconveniences because connections are disconnected even when the route is temporarily down.
    • If keepalive messages are disabled, sessions may hang indefinitely on the server, leaving "ghost" users and consuming server resources.

    Supported Protocols

    Specifies which SSH versions are supported by sshd. You can enable support for only version 2, or you can enable support for both versions 2 and 1 (with version 2 being the preferred choice).

    Barracuda Networks recommends that you only enable support for SSH version 2 because version 1 is vulnerable to man-in-the-middle attacks. By default, the Barracuda Networks client tries to use version 2.

    This setting is only available in Advanced View mode.

  4. To configure settings that are specific to each SSH version, click Advanced Setup from the Configuration menu in the left navigation pane.
    SSH Version 2 Options

    For SSH version 2, you can configure the following settings in the Protocol Version 2 Options section:

    Setting Description

    Allow Compression

    Specifies if compression should be enabled or disabled for SSH clients.

    Force Key Authentication

    Specifies if key usage is mandatory or optional for SSH clients.

    If key usage is mandatory for external SSH clients and you want to automate user logins, the private key of the client certificate on the Windows system must be generated in a UNIX compatible format. For instructions on how to generate the required key, see the following Handling Forced Key Authentication section.

    This setting is only available in Advanced View mode.

    Secure FTP Support

    Specifies if sshd implements the sftp subsystem. Secure FTP may be viewed as a more comfortable alternative to the humble scp command when trying to transfer bulk data to or from the box.

    This setting is only available in Advanced View mode.

    SSH Version 1 Options

    For SSH version 1, you can configure the following settings in the Protocol Version 1 Options section:

    Setting Description

    Server Key Length (Bits)

    Defines the number of bits in the ephemeral protocol version 1 server key. The minimum value is 512, and the default is 768.

    Key Regeneration Period

    Specifies the interval in seconds that the ephemeral server key is automatically regenerated after being used. Regenerating the key prevents the decryption of captured sessions if the keys are stolen. The key is only stored in memory.

    If you do not want the key to be regenerated, enter 0. The Barracuda Networks default is 900 (seconds).

  5. Click Send Changes and Activate.

Handling Forced Key Authentication

For various administrative purposes (such as collecting statistics with external tools), it may be desired to randomly connect to a system with an external SSH client, thereby omitting user interaction. Using the Microsoft Management Console (MMC), you can export a private key in encrypted PFX file format from the Certificate Store. However, this file is not usable by the Barracuda CloudGen Firewall. You must convert the PFX file to an unencrypted private key in PEM format. 

Step 1. Create an Administrative Login
  1. Go to CONFIGURATION > Full Configuration > Box Administrators.
  2. Click + to add a new administrative account.
  3. Enter a name for the account and click OK.
  4. In the Administrator Authentication section of the Administrators window, set Authentication Level to Key
  5. Import the public RSA key that has been issued for this user from the Microsoft Certificate Management Store.
Step 2. Export the Private Key from the Certificate Management Store
  1. On the Windows client, open the Certificate Management Store. At the DOS prompt, enter:
    • C:\windows\system32\certmgr.msc
  2. Browse to Personal > Certificates.
  3. Right-click the certificate and select All Tasks > Export.
  4. In the Certificate Export Wizard, select Yes to export the private key.
  5. In the PKCS #12 tab, clear the Enable strong protection check box.
  6. Enter a password.
  7. Specify a file name. For example, private_key.pfx
3. Copy the PKCS12 (.pfx) file to a UNIX Client Supporting OpenSSL

Copy the PFX file to a UNIX client that supports OpenSSL, such as the Barracuda CloudGen Firewall.

4. Convert the RSA Key from PKCS12 Format to PEM Format (encrypted)

On the UNIX client, browse to the RSA key. At the command line, enter:

  • # openssl pkcs12 -in private_key.pfx 
  • -nocerts -out priv.key

where priv.key specifies the file name after conversion.

5. Extract the Private Key and Generate an OpenSSH SSH-2 Private Key (unencrypted)

At the command line, enter:

  • # openssl rsa -in priv.key > ~/.ssh/
  • id_rsa_my_priv_key

where id_rsa_my_priv_key specifies the file name after decryption, and ~/.ssh/ is an arbitrarily chosen path on the UNIX client.

6. Log into the Barracuda CloudGen Firewall

At the command line, enter:

  • # ssh -i ~/.ssh/id_rsa_my_priv_key
  • -lloginname dest-ip

where loginname specifies the name of the administrative account as defined in Step 1, and dest-ip specifies the Barracuda CloudGen Firewall’s login IP address.

Depending on the client that the key was converted on, you may need to change the file permissions of the private key file. If the gateway refuses to use the key, change the file permissions of the key by entering:

  • chmod 600 ~/.ssh/id_rsa_my_priv_key

 

You can use the transformed private key with third-party remote SSH clients. For example, you can use it with SSH agents or import it into PuTTYGen for conversion into the file format for PuTTY (.ppk).

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