A simpler way to assess the network exposure of EC2 instances: AWS releases new network reachability assessments in Amazon Inspector

Performing network security assessments allows you to understand your cloud infrastructure and identify risks, but this process traditionally takes a lot of time and effort. You might need to run network port-scanning tools to test routing and firewall configurations, then validate what processes are listening on your instance network ports, before finally mapping the IPs identified in the port scan back to the host’s owner. To make this process simpler for our customers, AWS recently released the Network Reachability rules package in Amazon Inspector, our automated security assessment service that enables you to understand and improve the security and compliance of applications deployed on AWS. The existing Amazon Inspector host assessment rules packages check the software and configurations on your Amazon Elastic Compute Cloud (Amazon EC2) instances for vulnerabilities and deviations from best practices.

The new Network Reachability rules package analyzes your Amazon Virtual Private Cloud (Amazon VPC) network configuration to determine whether your EC2 instances can be reached from external networks such as the Internet, a virtual private gateway, AWS Direct Connect, or from a peered VPC. In other words, it informs you of potential external access to your hosts. It does this by analyzing all of your network configurations—like security groups, network access control lists (ACLs), route tables, and internet gateways (IGWs)—together to infer reachability. No packets need to be sent across the VPC network, nor must attempts be made to connect to EC2 instance network ports—it’s like packet-less network mapping and reconnaissance!

This new rules package is the first Amazon Inspector rules package that doesn’t require an Amazon Inspector agent to be installed on your Amazon EC2 instances. If you do optionally install the Amazon Inspector agent on your EC2 instances, the network reachability assessment will also report on the processes listening on those ports. In addition, installing the agent allows you to use Amazon Inspector host rules packages to check for vulnerabilities and security exposures in your EC2 instances.

To determine what is reachable, the Network Reachability rules package uses the latest technology from the AWS Provable Security initiative, referring to a suite of AWS technology powered by automated reasoning. It analyzes your AWS network configurations such as Amazon Virtual Private Clouds (VPCs), security groups, network access control lists (ACLs), and route tables to prove reachability of ports. What is automated reasoning, you ask? It’s fancy math that proves things are working as expected. In more technical terms, it’s a method of formal verification that automatically generates and checks mathematical proofs, which help to prove systems are functioning correctly. Note that Network Reachability only analyzes network configurations, so any other network controls, like on-instance IP filters or external firewalls, are not accounted for in the assessment. See documentation for more details.

Tim Kropp, Technology & Security Lead at Bridgewater Associates talked about how Bridgewater benefitted from Network Reachability Rules. “AWS provides tools for organizations to know if all their compliance, security, and availability requirements are being met. Technology created by the AWS Automated Reasoning Group, such as the Network Reachability Rules, allow us to continuously evaluate our live networks against these requirements. This grants us peace of mind that our most sensitive workloads exist on a network that we deeply understand.”

Network reachability assessments are priced per instance per assessment (instance-assessment). The free trial offers the first 250 instance-assessments for free within your first 90 days of usage. After the free trial, pricing is tiered based on your monthly volume. You can see pricing details here.

Using the Network Reachability rules package

Amazon Inspector makes it easy for you to run agentless network reachability assessments on all of your EC2 instances. You can do this with just a couple of clicks on the Welcome page of the Amazon Inspector console. First, use the check box to Enable network assessments, then select Run Once to run a single assessment or Run Weekly to run a weekly recurring assessment.
 

Figure 1: Assessment setup

Customizing the Network Reachability rules package

If you want to target a subset of your instances or modify the recurrence of assessments, you can select Advanced setup for guided steps to set up and run a custom assessment. For full customization options including getting notifications for findings, select Cancel and use the following steps.

1. Navigate to the Assessment targets page of the Amazon Inspector console to create an assessment target. You can select the option to include all instances within your account and AWS region, or you can assess a subset of your instances by adding tags to them in the EC2 console and inputting those tags when you create the assessment target. Give your target a name and select Save.
    
   
   

   Figure 2: Assessment target

   Optional agent installation: To get information about the processes listening on reachable ports, you’ll need to install the Amazon Inspector agent on your EC2 instances. If your instances allow the Systems Manager Run command, you can select the Install Agents option while creating your assessment target. Otherwise, you can follow the instructions here to install the Amazon Inspector agent on your instances before setting up and running the Amazon Inspector assessments using the steps above. In addition, installing the agent allows you to use Amazon Inspector host rules packages to check for vulnerabilities and security exposures in your EC2 instances.

2. Go to the Assessment templates page of the Amazon Inspector console. In the Target name field, select the assessment target that you created in step 1. From the Rules packages drop-down, select the Network Reachability-1.1 rules package. You can also set up a recurring schedule and notifications to your Amazon Simple Notification Service topic. (Learn more about Amazon SNS topics here). Now, select Create and Run. That’s it!
   

   Alternately, you can run the assessment by selecting the template you just created from the Assessment templates page and then selecting Run, or by using the Amazon Inspector API.

You can view your findings on the Findings page in the Amazon Inspector console. You can also download a CSV of the findings from Amazon Inspector by using the Download button on the page, or you can use the AWS application programming interface (API) to retrieve findings in another application.

Note: You can create any CloudWatch Events rule and add your Amazon Inspector assessment as the target using the assessment template’s Amazon Resource Name (ARN), which is available in the console. You can use CloudWatch Events rules to automatically trigger assessment runs on a schedule or based on any other event. For example, you can trigger a network reachability assessment whenever there is a change to a security group or another VPC configuration, allowing you to automatically be alerted about insecure network exposure.

Understanding your EC2 instance network exposure

You can use this new rules package to analyze the accessibility of critical ports, as well as all other network ports. For critical ports, Amazon Inspector will show the exposure of each and will offer findings per port. When critical, well-known ports (based on Amazon’s standard guidance) are reachable, findings will be created with higher severities. When the Amazon Inspector agent is installed on the instance, each reachable port with a listener will also be reported. The following examples show network exposure from the Internet. There are analogous findings for network exposure via VPN, Direct Connect, or VPC peering. Read more about the finding types here.

Example finding for a well-known port open to the Internet, without installation of the Amazon Inspector Agent:
 

Figure 3: Finding for a well-known port open to the Internet

Example finding for a well-known port open to the Internet, with the Amazon Inspector Agent installed and a listening process (SSH):
 

Figure 4: Finding for a well-known port open to the Internet, with the Amazon Inspector Agent installed and a listening process (SSH)

Note that the findings provide the details on exactly how network access is allowed, including which VPC and subnet the instance is in. This makes tracking down the root cause of the network access straightforward. The recommendation includes information about exactly which Security Group you can edit to remove the access. And like all Amazon Inspector findings, these can be published to an SNS topic for additional processing, whether that’s to a ticketing system or to a custom AWS Lambda function. (See our blog post on automatic remediation of findings for guidance on how to do this.) For example, you could use Lambda to automatically remove ingress rules in the Security Group to address a network reachability finding.

Summary

With this new functionality from Amazon Inspector, you now have an easy way of assessing the network exposure of your EC2 instances and identifying and resolving unwanted exposure. We’ll continue to tailor findings to align with customer feedback. We encourage you to try out the Network Reachability Rules Package yourself and post any questions in the Amazon Inspector forum.

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