Use AWS Firewall Manager and VPC security groups to protect your applications hosted on EC2 instances

Apr 25 2020

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You can use AWS Firewall Manager to centrally configure and manage Amazon Virtual Private Cloud (Amazon VPC) security groups across all your AWS accounts. This post will take you through the step-by-step instructions to apply common security group rules, audit your security groups, and detect unused and redundant rules in your security groups across your AWS environment.

In this post, I’ll show you how to create and enforce a master set of security group rules by using common security group policy, while still allowing developers to deploy and manage application-specific security group rules. In the example below, the security group rules you’ll create allow SSH access only from the public IP address of the bastion host, and to set a policy that prohibits any security group rules that allow SSH access from everywhere (port 22).

When you use Firewall Manager to centrally apply a common security group, you can do things such as ensure that all Application Load Balancers only talk to Amazon CloudFront, or the Secure Shell (SSH) protocol is only allowed from specific IP ranges, or to give system administrators access to a central database.

In many organizations, developers write their own security group rules for their applications. However, if you’re a security administrator, you want to audit the security group rules so you’ll know when a security group is misconfigured. Using audit security group policy, you can set guardrails on which security group rules can or cannot be created across your organization. For example, you could only allow security group rules on ports 10-1000, or specify that you do not allow security group rules on port 23.

As an administrator, you also want to simplify operations by detecting unused and redundant security groups across their AWS accounts. You can use a managed audit policy to help identify unused and redundant security groups.

If you haven’t used these services before, here’s a quick overview:

AWS Firewall Manager is a security management service that allows you to centrally configure and manage firewall rules across your accounts and applications in AWS Organization by using AWS Config in the background. Using AWS Firewall Manager, you can easily roll out AWS WAF rules, create AWS Shield Advanced protections, and enable security groups for your Amazon Elastic Compute Cloud (Amazon EC2) and elastic network interface resource types in Amazon VPCs.
VPC security groups act as a virtual, stateful firewall for your Amazon Elastic Compute Cloud (Amazon EC2) instance to control inbound and outbound traffic. You can specify separate rules for inbound and outbound traffic, and instances associated with a security group can’t talk to each other unless you add rules allowing it.

After you put the master set of security group rules in place, you’ll get notification of all non-compliant changes made by the developers. You can take remediation action if necessary using an audit security group policy. In this post, you’ll also set up a usage security group policy, so that you can flag unused security groups and merge redundant security groups for simpler administration.

Prerequisites

AWS Firewall Manager has the following prerequisites:

AWS Organizations: Your organization must be using AWS Organizations to manage your accounts, and All Features must be enabled. For more information, see Creating an Organization and Enabling All Features in Your Organization.
An administrator AWS Account: You must designate one of the AWS accounts in your organization as the administrator for Firewall Manager. This gives the account permission to deploy AWS WAF rules across the organization.
AWS Config: You must enable AWS Config for all of the accounts in your organization, so that AWS Firewall Manager can detect newly created resources. To enable AWS Config for all of the accounts in your organization, you can use the Enable AWS Config template on the StackSets Sample Templates page. For more information, see Getting Started with AWS Config.

Note: You’ll be charged $100 per policy per month. In the solution in this post, you’ll create three policies. In addition, AWS Config charges also apply. For more information, see AWS Firewall Manager pricing and AWS Config pricing.

Overview

The diagram below illustrates the following steps:

Complete the prerequisites that were outlined in the prerequisites section above.
Create a primary security group under AWS Firewall Manager. This is a VPC security group that gets replicated as a new security group to every resource within the policy scope.
In AWS Firewall Manager, create policies that can be applied to individual application security groups by mapping them to specific application name/value tags. The policies you create will result in the generation of individual new security groups.
Application developers can build additional app-specific security group rules created in the previous step.

Figure 1: Overview of solution

Create a common security group policy

You’ll begin by creating a common security group policy to push primary security group rules across all accounts.

Sign in to the AWS Management Console using the AWS Firewall Manager administrator account that you set up in the prerequisites, and then open the Firewall Manager console.
In the navigation pane, under AWS Firewall Manager, choose Security policies.
Using the Filter menu, select the AWS Region where your application is hosted and choose Create policy. In my example, I choose US West (Oregon).
For Policy type, choose Security group.
For Security group policy type, choose Common security groups, then choose Next.
Enter a policy name. In my example, I’ve named my policy Test_Common_Policy.
Policy rules allow you to choose how the security groups in this policy are applied and maintained. For this tutorial, choose Apply the primary security groups to every resource within the policy scope and leave the other options unchecked. You can also choose to apply only one of these policies. Note that if you choose both check boxes, a local user won’t be able to modify security group and they won’t be able to add additional security groups.
Choose Add primary security group to see all security groups in your account in your specified AWS Region. Select any one of your existing security groups, or create a new security group.
(Optional) If you choose to create a new security group, you’ll be taken to the VPC dashboard where you can create your primary security group by following the Creating a Security Group documentation. Under audit security group, add the following:
1. For Ingress Rules, choose Allow access on Port 22 from 203.0.113.1/32.
2. For Egress Rules, choose Allow all traffic on all ports.
After you select the primary security group, choose Add security group.
For Policy action, for this example, choose Apply policy rules and identify resources that are non-compliant but do not auto remediate. By selecting this option, Firewall Manager will notify you of any non-compliant security groups, but will not auto-remediate. Choose Next.
For Policy scope, select the following:
1. For AWS accounts included in this policy, choose All accounts under my organization.
2. For Resource Type to apply this policy, choose EC2 instances.
3. For Criteria to select the resources to protect, choose Include only resources that have the specified tags.
4. For Key, enter Env.
5. For Value, enter Prod.
Choose Next.
Review the security policy, then choose Create policy.

Figure 2: Summary of Common Security Group policy

The security policy will review all the EC2 instances in your child accounts in your specified AWS Region and add the primary security group to the primary network interface of the Amazon EC2 instances. All primary interfaces of the Amazon EC2 instances created in future will also have this primary security group. If the developers remove the security group rules of the primary security group, you’re notified when Firewall Manager Service marks the resource as non-compliant. You can then take remediation action of changing the security policy action to Apply policy rules and auto remediate any non-compliant resources and the non-compliant security group rules will be removed. Alternatively, you can check the non-compliant resources, then log into the AWS account and take remediation action manually.

Create an audit security group policy

Now, you’ll create an audit security group policy to enforce the guardrails. You’ll create a security group rule that allows port 22 access from an allowed IP subnet of 203.0.113.1/32 according to the security team’s recommendations.

In the AWS Management Console, select AWS WAF and AWS Shield.
In the navigation pane, under AWS Firewall Manager, choose Security policies.
In the Filter, select the AWS Region where your application is hosted and choose Create policy. In my example, I will choose US West (Oregon).
For Policy type, choose Security group. For Security group policy type, choose Auditing and enforcement guidelines for security group rules, then choose Next.
Enter a policy name. In my example, I’ve named my policy Test_Audit_Policy.
For Policy rules, select Allow any rules defined in audit security group.
Choose Add audit security group to see all security groups in your account in your specified AWS Region. You can select a security group, or create a new security group.
(Optional) If you choose to create a new security group, you’ll be taken to VPC dashboard where you can create your primary security group by following the Creating a Security Group documentation. In the audit security group, add the following:
1. For Ingress Rules, choose Allow access on Port 22 from 203.0.113.1/32.
2. For Egress Rules, choose Allow all traffic on all ports.
After you select the audit security group, choose Add security group.
For Policy action, you can only select Apply policy rules and identify resources that are non-compliant but do not auto remediate. By selecting this option, Firewall Manager will notify you of any non-compliant security groups, but will not auto-remediate. Choose Next.
For Policy scope, select the following:
1. For AWS accounts included in this policy, choose All accounts under my organization.
2. For Resource type to apply this policy, choose Security groups.
3. For Criteria to select the resources to protect, choose Include only resources that have the specified tags.
4. For Key, enter Env.
5. For Value, enter Prod.
Choose Next.
Review the security policy and choose Create policy.

Figure 3: Summary of Audit Security Group policy

The security policy will audit all the security groups in your child accounts in your specified AWS Region and will only allow security group ingress rules that allow port 22 access from 203.0.113.1/32. All security groups created in future will also have this restriction. If Firewall Manager detects that a security groups exists that allows port 22 access from everywhere except 203.0.113.1/32, you’re notified when Firewall Manager Service marks the resource as non-compliant. You can then take remediation action of editing the security policy action to Apply policy rules and auto remediate any non-compliant resources and the non-compliant security group rules will be removed. Alternatively, you can check the non-compliant resources, then log into the AWS account and take remediation action manually.

Create a usage security group policy

Lastly, you’ll create a usage security group policy to remove unused security groups, and to merge redundant security groups.

In the AWS Management Console, select AWS WAF and Shield.
In the navigation pane, under AWS Firewall Manager, choose Security policies. In the Filter, select the AWS Region where your application is hosted and choose Create policy. In my example, I am choosing US West (Oregon).
For Policy type, choose Security group. For Security group policy type, choose Auditing and cleanup of unused and redundant security groups. Choose Next.
Enter a policy name. In my example, I’ve named my policy Test_Usage_Policy.
For Policy rules, select both the options: Security groups within this policy scope should be used by at least one resource and Security groups within this policy scope should not have similar content.
For Policy action, select Apply policy rules and identify resources that are non-compliant but do not auto remediate. Choose Next.
For Policy scope, select the following:
1. For AWS accounts included in this policy, choose All accounts under my organization.
2. For Resource type to apply this policy, choose Security groups.
3. For Criteria to select the resources to protect, choose Include only resources that have the specified tags.
4. For Key, enter Env.
5. For Value, enter Prod.
Choose Next.
A pop-up warning message will appear. Select Exclude Firewall Manager admin account from the policy scope, so that security groups in the administrator account are not affected.
Review the security policy and choose Create policy.

Figure 4: Summary of Usage Security Group policy

The security policy will review all the security groups in your child accounts in your specified AWS Region and check if there are any security groups that are not associated with any resource. The security policy will also review if there are any duplicate security group rules. After these cases are identified, AWS Firewall Manager will automatically merge them into one security group. All security groups created in future will also be checked for this. If Firewall Manager detects that a security groups exists that is not associated to any resource or has overlapping rules, you’ll be notified when Firewall Manager Service marks the resource as non-compliant. You can then take remediation action of editing the security policy action to Apply policy rules and auto remediate any non-compliant resources and the non-compliant security group rules will either be removed (in case of unused) or rules will be merged (in case of redundant security groups). Alternatively, you can check the non-compliant resources, then log into the AWS account and take remediation action manually.

Conclusion

In this post, you learned how you can create AWS Firewall Manager rules using the console. Using both VPC security groups and AWS Firewall Manager, you created a deployment strategy that enables the developers in your organization to maintain a security mindset and begin coding security group rules, while at the same time ensuring that all applications are still protected by a set of security group rules defined by your organization’s security team. In addition, you have reduced the likelihood of misconfigured or overly permissive security groups, as well as the operational burden, by simplifying the security groups created in all your member accounts.

For further reading, see AWS Firewall Manager Update – Support for VPC Security Groups.

If you have feedback about this post, submit comments in the Comments section below. If you have questions about this post, start a new thread on the AWS Firewall Manager forum or contact AWS Support.

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