Hardening ScreenOS

Posted on 2016-10-18
Last Modified: 2016-10-28
Hello to All of you ,
my supervisor has assigned a new task: write an hardening guide for the operating System ScreenOs installed on Netscreen firewall.

I'm totally new to netscreen and I would like to ask you if you could provide me some link to start with, then , if it's fine for you I can share the document and we could review it.

Can it be a good way to proceed ?
thank you
Question by:carlettus
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LVL 69

Assisted Solution

Qlemo earned 500 total points
ID: 41849637
Hardening means to reduce the attacker surface. That is, you switch off "unsecure" configuration means like HTTP and Telnet, and allow SSH and HTTPS only. Plus use a secure admin password. And allowing configuration access only from LAN, of course (on the corresponding interface).

The other task is to make the firewall as closed as possible against access from Internet. By default nothing is allowed to pass from WAN to LAN, but you also need to enable different screening features on the corresponding interface. Screening checks for typical attacks like port scans, and blocks access temporarily if detected to prevent further attacks or investigations. Background is that you can get a profile of the firewall OS by the replies to attack packets, and that again allows to craft a more dedicated attack. Screening can help to not allow for a profile.

Author Comment

ID: 41850305
Hello and thank you for your message.
I was looking something specific related to Netscreen ScreenOs , this looks a good start

I'll write down the document and post for your considerations.
Thank you

Author Comment

ID: 41859862
these are some topics I'm writing down for hardening netscreen firewall and ScreenOs
Can you confirm all it's correct?
Thank you


The AUX port access to the firewall is possible only via a modem and by default, this setting is off on the firewall for security reasons.
To enable this functionality, enable
ns->set int ser0/0 modem dial-in enable.

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2)Disable Telnet
In order to disable telnet you need to perform the following actions.
ns-> unset interface <zone_name> manage telnet

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3) Reduce console  timeout
You can also modify the console timeout option via the CLI by typing set console timeout 5. Note that a timeout value of 0 will disable the timeout feature. Use the get console command to verify the change
ns-> set console timeout 5
ns-> get console 

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Output of get console to confirm the change

Console timeout: 5(minute), Page size: 22/22, debug: buffer
privilege 250, config was changed and not saved!
ID State Duration Task Type Host
0 Login 660 13433716 Telnet
1 Logout 0 13435768 Local
2 Logout 0 13424824 Local
3 Logout 0 13410460 Local

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3) Convert SSH V1 to SSH V2 and Enable SSH
If ssh v1 was initially configured on the firewall, then all SSH keys from version 1 must be deleted. “delete ssh device all”

ns-> set ssh disabled 
ns-> delete ssh device all

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Output netscreen
    SSH disabled for vsys: 1

    PKA keys deleted from device: 0
    Host keys deleted from device: 1

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Execute the 'set ssh version v2' command to activate SSH v2 for the device.
ns-> set ssh version v2

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   SSH version 2 has been activated.
Then, enable SSH:
ns-> set ssh enable

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View the SSH configurations settings with the command 'get ssh'.  Note that it should report it is 'active' and 'enabled':
ns-> get ssh
SSH V2 is active
SSH is enabled
SSH is ready for connections
Maximum sessions: 3
Active sessions: 1

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LVL 69

Accepted Solution

Qlemo earned 500 total points
ID: 41860873
1) is wrong. You want to do exactly the opposite - disable AUX.
2) it is <interface_name>, not <zone_name>

I would add force redirecting HTTP to HTTPS
And how about disabling HTTP (resp. force redirect to HTTPS)?
set admin http redirect
set ssl enable

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but that also requires that you use and assign at least a self-signed certifcate, which is best done via WebUI.

And how about only enabling access on the Trust interface (no Internet config access)?

Author Comment

ID: 41861656
great Qlemo ...
I'm still working on it and today i'll post the rest .
Thank you this is what I really need .
Ciao from Italy

Assisted Solution

carlettus earned 0 total points
ID: 41862255
thank you again . Here are some other points I want to point out.
Can you please confirm that the snmp configuration is correct ?
Thank you

4) Limit system access to your firewall

The firewall administrator should limit which IP addresses are authorized to perform management services on the OS.
To add a permitted IP address via the CLI the command to use is [set admin manager-ip]

ns->set admin manager-ip

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5) Secure root account

The root admin account is the most privileged account. It can
create and delete other admin accounts, virtual systems and modify certain
aspects of virtual systems.This account can only be stored locally on the firewall,
and there must be at least one root admin.
All ScreenOS devices ship with the default username netscreen and the default password netscreen for the root level account. It’s important to change both username and password for root admin account.

ns-> set admin name admin-string
ns-> set admin password password-string

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It is recommended to create a read-write administrator (super) to use for regular maintenance.
If that administrator is compromised, there will be no direct root access to the device.

ns-> set admin user super password password-string privilege all
ns-> set admin auth server local

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It is recommended to create a read-only administrator (ro-admin). This administrator can only view the configuration and some debugging features are restricted.

ns-> set admin user ro-admin password password-string privilege "read-only"
ns-> set admin auth server local

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6) Backup configuration

Save the existing configuration to an TFTP server with the command:
ns-> save config to tftp <tftp_server_ip> <config_filename>

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7) Snmp implementation ad enforcement

Juniper Networks security devices support SNMPv1, SNMPv2c by default. Security devices are not shipped with a default configuration for SNMPv3, it’s important to configure SNMPV3 in order to implement authentication and encryption not present in the previous versions.

In order to configure the community name and assign privileges type of read-only :
ns-> set snmp community adminro read-only version v3

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Configure a SNMP host that will be allowed to access the Juniper firewall device using the community adminro type:

ns-> set snmp host adminro trap v3

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LVL 69

Assisted Solution

Qlemo earned 500 total points
ID: 41862406
7) is fine, and the other points are correct and valid.

Author Closing Comment

ID: 41863728
Thank you , I've just passe the document to my supervisor.
All should be fine. I'll come back if there will be changes .
This cross check was useful.

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