web analytics

Archive for the ‘Firewall’ Category

Managing network security aspects in the public cloud

Managing cloud environments on large scale has many challenges.

One of the challenges many organizations are facing is managing network inbound/outbound network connectivity to their cloud environments.

Due to the nature of the public cloud, all resources are potentially public, unless we configured them otherwise.

What are the challenges in the network security domain?

There are many challenges related to network security, here are the most common ones:

  • Unauthorized inbound network access – Publicly facing resources (such as virtual machines, object storage, databases, etc.) allowing anyone on the Internet access to the resources
  • Unrestricted outbound network access – Internal resources (such as virtual machines, databases, serverless, etc.) can initiate outbound traffic to resources on the public Internet
  • Managing network access rules at large scale – Ability to control thousands of firewall rules created over time, while managing multiple accounts for a specific cloud provider (or even multiple different cloud providers)
  • Understanding the network attack surface – Ability to get a clear view of what inbound or outbound traffic is allowed or denied in a large cloud environment with multiple accounts
  • Enabling the business, while keeping the infrastructure secure – Ability to respond to multiple business requests, using small network/information security / IT team

With all the above challenges, how do we keep our cloud network infrastructure secure and at a large scale?

Set Guardrails

One of the common ways to configure guardrails is to use organizational policies using Policy-as-Code.

All major cloud providers support this capability.

It allows us to configure rules for the maximum allowed permissions over our cloud environments according to our company security policy while allowing developers / DevOps to continue provisioning resources.

AWS Service control policies (SCPs)

Below are sample service control policies that can be configured at the AWS organizational level (with inheritance to the underlining OU’s), for restricting inbound access:

Azure Policy

Below are sample Azure policies that can be configured at the Azure subscription level, for restricting inbound access:

Google Organization Policies

Below are sample Google organization policies that can be configured at the GCP Project level, for restricting inbound access:

Controlling inbound/outbound network traffic at scale

At large scale, we cannot rely on the built-in layer 4 access control mechanisms (such as AWS Security groups, Azure Network Security Groups, or GCP Firewall Rules) to define inbound or outbound traffic from/to our cloud environments.

For large scale, we should consider alternatives that will allow us to configure network restrictions, while allowing us central visibility over our entire cloud environment.

Another aspect we should keep in mind is that the default layer 4 access control mechanisms do provide us advanced protection against today’s threats, such as the ability to perform TLS inspection, control web traffic using URL filtering, etc.

Cloud-native firewall services:

Note: If you prefer to use 3rd party NGFW, you can deploy it using AWS Gateway Load Balancer or Azure Gateway Load Balancer.

Additional references

Understanding the network attack surface

One of the common issues with large cloud environments is to have a visibility of which inbound or outbound ports are opened to the Internet, exposing the cloud environment.

Common services to allow network visibility:

Another alternative for getting insights into attack surface or network misconfiguration is to deploy 3rd party Cloud Security Posture Management (CSPM) solution, which will allow you central visibility into publicly accessible virtual machines, databases, object storage, and more, over multiple cloud providers’ environments.


In this blog post, I have presented common challenges in managing network security aspects in cloud environments.

Using a combination of organizational policies, strict inbound/outbound traffic control, and good visibility over large or complex cloud environments, it is possible to enable the business to move forward, while mitigating security risks.

As the cloud threat landscape evolves, so do security teams need to research for suitable solutions to enable the business, while keeping the cloud environments secure.

Hardening guide for Cisco Firewall (PIX, ASA, FWSM)

Important note
The guide bellow instructs how to secure Cisco Firewall (PIX, ASA, FWSM).
Not all commands will work on every device series or on every IOS version.
It is highly recommended to test each setting in a test lab before implementing changes to production systems.

Hardening phase
Configure AAA Authentication for Enable Mode (ASA, FWSM, PIX):
aaa authentication enable console LOCAL

Configure AAA Authentication for Console and VTY Lines (ASA, FWSM, PIX):
aaa authentication serial console LOCAL
aaa authentication ssh console LOCAL
aaa authentication http console LOCAL

Configure Local Password (ASA, FWSM, PIX):
passwd <login_password> encrypted

Configure ASDM Access Control (ASA, FWSM, PIX):
http <remote_ip_address> <remote_subnet_mask> <interface_name>

Configuring SSH (ASA, FWSM, PIX):
hostname <device_hostname>
domain-name <domain-name>
crypto key generate rsa modulus 2048

Configure SSH for Remote Device Access (ASA, PIX):
no telnet <interface_name>
ssh <remote_ip_address> <remote_subnet_mask> <interface_name>
ssh version 2

Configure Timeout for Login Sessions (ASA, FWSM, PIX):
console timeout 10
ssh timeout 10

Configure Local User and Encrypted Password (ASA, FWSM, PIX):
username <local_username> password <local_password> encrypted

Configure Enable Password (ASA, FWSM, PIX):
enable password <enable_password> encrypted

Disable SNMP Read Access (ASA, FWSM, PIX):
clear configure snmp-server
no snmp-server host <interface_name> <remote_ip_address>

Disable SNMP Traps (ASA, FWSM, PIX):
no snmp-server enable traps all

Configure Clock Time Zone (ASA, PIX):
clock timezone GMT <hours offset>

Disable DHCP Server Service (ASA, FWSM, PIX):
clear configure dhcpd
no dhcpd enable <interface_name>

Disable HTTP Service (ASA, FWSM, PIX) – in-case not in use:
no http server enable <port>

Configure Console Logging Severity Level (ASA, FWSM, PIX):
logging console critical

Configure Timestamps in Log Messages (ASA, FWSM, PIX):
logging timestamp

Configure AAA Flood Guard (FWSM, PIX):
floodguard enable

Configure Fragment Chain Fragmentation Checks (ASA, FWSM, PIX):
fragment chain 1 <interface_name>

Configure Protocol Inspection (FWSM, PIX):
fixup protocol ftp <port>
fixup protocol http <port>
fixup protocol smtp <port>

Configure Protocol Inspection (ASA):
inspect ftp [map_name]
inspect http [map_name]
inspect esmtp [map_name]

Configure Unicast Reverse-Path Forwarding (ASA, FWSM, PIX):
interface <interface_id>
ip verify reverse-path interface <interface_name>

Save the changes: