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Can SonicWall firewalls prevent brute force attacks?

Description

The scope of this article is to describe some of the best practices a network administrator can apply to protect the firewall and the network behind it from bruteforce or dictionary attacks.

A brute force attack is a method used to obtain information such as a user password or personal identification number (PIN) by trying thousands of combinations. In a brute force attack, automated software is used to generate a large number of consecutive guesses as to the value of the desired data.

A dictionary attack is a method of using a dictionary in order to get access to a computer or server by systematically entering every word in a dictionary as a password. It can also be used to decrypt encrypted messages by guessing the key.

The Intrusion Prevention System (IPS) available in the SonicWall, if enabled on the WAN zone, should prevent most of the exploits, web attacks, SQL injections and database attacks. In order to prevent them, the SonicWall will match the traffic pattern against the IPS signatures and if it matches the traffic will be blocked.

NOTE: IPS must be licensed and the signatures must be up-to-date.

However, some bruteforce attacks are not easy to be detected as they look like normal attempts to login. This article contains best practices to avoid bruteforce attacks towards your network.

Resolution

Here's some of the best practices to respect in order to have the best protection against this type of attacks:

  • Make sure IPS is licensed and enabled from Security Services | IPS and on the WAN zone from Network | Zones. You will need to make sure that the database is correctly downloaded and there's nothing blocking the updates.
    Image
  • Ensure that IPS is preventing (blocking) all med/high attacks:
    Image

    NOTE: DPI-SSL should also be licensed and configured so attacks via HTTPS/SSH can be easily detected:

  • Geo-IP and Botnet Filter can also help on this fight
  • Enable TCP, UDP, ICMP Flood Protection on Firewall Settings | Flood Protection.
  • If you wish to have access to the WAN Interface via SSH or HTTPS, you may create an access rule (Firewall | Access Rules) from WAN to WAN denying all traffic but the HTTPS/SSH traffic from specific Public IPs of your company.
  • On System | Administration
    • enable Enable administrator/user lockout
    • enable Password must be changed every (days):
    • enable Bar repeated passwords for this many changes:
    • Set the Enforce password complexity: to Require alphabetic, numeric and symbolic characters and set the complexity requirements.
    • Change the default HTTPS and SSH Ports for management 443 to a custom one.
      Image

      CAUTION: Be very careful about enabling the "administrator/user lockout"! Some bruteforce attacks are actually DoS, attackers are just trying to lockout a huge number of your most important users so that your network will be down.

  • Use VPNs (SSLVPN or IPSec VPN) to secure access to internal servers should you need RDP or get access to them.You shouldn't open ports like RDP - 3389 to the whole world using a NAT Policy unless you're filtering the access via Access Rules to only known Public IPs.
  • Do not use the option "Use default key for simple client provisioning" or "Cache XAUTH User Name and Password on Client:" on the VPN | Settings and use Strong Encryption Methods.
  • Enable the 2 Factors Authentication for external connecting users (i.e. SSLVPN or GVC users): when creating Local Users from Users | Local Users, enable the option Require one-time passwords or enable it on your LDAP/Radius Servers.
  • Bruteforce/Dictionary attacks via SSLVPN can be blocked by using a SonicWall SRA Appliance: How to block Brute Force and Dictionary attacks with SRA

CAUTION: Accomplishing the best protection for your network against bruteforce and dictionary attacks would require the upstream ISP or services like CloudFlare, Incapsula, etc. to drop the traffic once a bruteforce attack against your network is detected.

By following the above best practices, you will harden your defenses.


Resolution for SonicOS 6.5 and Later

SonicOS 6.5 was released September 2017. This release includes significant user interface changes and many new features that are different from the SonicOS 6.2 and earlier firmware. The below resolution is for customers using SonicOS 6.5 and later firmware.

Here's some of the best practices to respect in order to have the best protection against this type of attacks:

  • Make sure IPS is licensed and enabled from Manage | Security Services | Intrusion Prevention and on the WAN zone from Manage | Network | Zones. You will need to make sure that the database is correctly downloaded and there's nothing blocking the updates.
    Image
  • Ensure that IPS is preventing (blocking) med/high attacks:
    Image

    NOTE: DPI-SSL should also be licensed and configured so attacks via HTTPS/SSH can be easily detected:

  • Enabling Geo-IP and Botnet Filter security services can also help prevent brute force attacks.
  • Enable TCP, UDP, ICMP Flood Protection on Manage | Firewall Settings | Flood Protection.
  • If you wish to have access to the WAN Interface via SSH or HTTPS, you may create an access rule (Manage | Rules | Access Rules) from WAN to WAN denying all traffic but the HTTPS/SSH traffic from specific Public IPs of your company.
  • On Manage | Appliance | Base Settings
    • enable Enable administrator/user lockout
    • enable Password must be changed every (days):
    • enable Bar repeated passwords for this many changes:
    • Set the Enforce password complexity: to Require alphabetic, numeric and symbolic characters and set the complexity requirements.
    • Change the default HTTPS and SSH Ports for management 443 to a custom one.
      Image

      CAUTION: Be very careful about enabling the "administrator/user lockout"! Some bruteforce attacks are actually DoS, attackers are just trying to lockout a huge number of your most important users so that your network will be down.

  • Use VPNs (SSLVPN or IPSec VPN) to secure access to internal servers should you need RDP or get access to them.You shouldn't open ports like RDP - 3389 to the whole world using a NAT Policy unless you're filtering the access via Access Rules to only known Public IPs.
  • Do not use the option "Use default key for simple client provisioning" or "Cache XAUTH User Name and Password on Client:" on the Manage | VPN | Base Settings and use Strong Encryption Methods.
  • Enable the 2 Factors Authentication for external connecting users (i.e. SSLVPN or GVC users): when creating Local Users from Manage | Users | Local Users & Groups, enable the option Require one-time passwords or enable it on your LDAP/Radius Servers.
  • Bruteforce/Dictionary attacks via SSLVPN can be blocked by using a SonicWall SRA Appliance: How to block Brute Force and Dictionary attacks with SRA

CAUTION: Accomplishing the best protection for your network against bruteforce and dictionary attacks would require the upstream ISP or services like CloudFlare, Incapsula, etc. to drop the traffic once a bruteforce attack against your network is detected.

By following the above best practices, you will harden your defenses.