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Security Best Practices for Amazon Web Services

By Rich

This is a short series on where to start with AWS security. We plan to release it as a concise white paper soon. It doesn’t cover everything but is designed to kickstart and prioritize your cloud security program on Amazon. We do plan to write a much deeper paper next year, but we received several requests for something covering the fundamentals, so here you go…

Building on a Secure Foundation

Amazon Web Services is one of the most secure public cloud platforms available, with deep datacenter security and many user-accessible security features. Building your own secure services on AWS requires properly using what AWS offers, and adding additional controls to fill the gaps.

Amazon’s datacenter security is extensive – better than many organizations achieve for their in-house datacenters. Do your homework, but unless you have special requirements you can feel comfortable with their physical, network, server, and services security. AWS datacenters currently hold over a dozen security and compliance certifications, including SOC 1/2/3, PCI-DSS, HIPAA, FedRAMP, ISO 27001, and ISO 9001.

Never forget that you are still responsible for everything you deploy on top of AWS, and for properly configuring AWS security features. AWS is fundamentally different than even a classical-style virtual datacenter, and understanding these differences is key for effective cloud security. This paper covers the foundational best practices to get you started and help focus your efforts, but these are just the beginning of comprehensive cloud security.

Defend the Management Plane

One of the biggest risks in cloud computing is an attacker gaining access to the cloud management plane: the web interface and APIs to configure and control your cloud. Fail to lock down this access and you might as well just hand over your datacenter to the bad guys.

Fortunately Amazon provides an extensive suite of capabilities to protect the management plane at multiple levels, including both preventative and monitoring controls. Unfortunately the best way to integrate these into existing security operations isn’t always clear; it can also be difficult to identify any gaps. Here are our start-to-finish recommendations.

Control access and compartmentalize

  • The most important step is to enable Multifactor Authentication (MFA) for your root account. For root accounts we recommend using a hardware token which is physically secured in a known location which key administrators can access in case of emergency.
  • Also configure your Security Challenge Questions with random answers which aren’t specific to any individual. Write down the answers and also store them in a secure but accessible location.
  • Then create separate administrator accounts using Amazon’s Identity and Access Management (IAM) for super-admins, and also turn on MFA for each of those accounts. These are the admin accounts you will use from day to day, saving your root account for emergencies.
  • Create separate AWS accounts for development, testing, and production, and other cases where you need separation of duties. Then tie the accounts together using Amazon’s consolidated billing. This is a very common best practice.

Locking down your root account means you always keep control of your AWS management, even in case an administrator account is compromised. Using MFA on all administrator accounts means you won’t be compromised even if an attacker manages to steal a password. Using different AWS accounts for different environments and projects compartmentalizes risks while supporting cross-account access when necessary.

Amazon’s IAM policies are incredibly granular, down to individual API calls. They also support basic logic, such as tying a policy to resources with a particular tag. It can get complicated quickly, so aside from ‘super-admin’ accounts there are several other IAM best practices:

  • Use the concept of least privilege and assign different credentials based on job role or function. Even if someone needs full administrative access sometimes, that shouldn’t be what they use day to day.
  • Use IAM Roles when connecting instances and other AWS components together. This establishes temporary credentials which AWS rotates automatically.
  • Also use roles for cross account access. This allows a user or service in one AWS account to access resources in another, without having to create another account, and ties access to policies.
  • Apply object-level restrictions using IAM policies with tags. Tag objects and the assigned IAM policies are automatically enforced.
  • For administrative functions use different accounts and credentials for each AWS region and service.
  • If you have a user directory you can integrate it with AWS using SAML 2.0 for single sign-on. But be careful; this is most suitable for accounts that don’t need deep access to AWS resources, because you lose the ability to compartmentalize access using different accounts and credentials.
  • Never embed Access Keys and Secret Keys in application code. Use IAM Roles, the Security Token Service, and other tools to eliminate static credentials. Many attackers are now scanning the Internet for credentials embedded in applications, virtual images, and even posted on code-sharing sites.

These are only a starting point, focused on root and key administrator accounts. Tying them to multifactor authentication is your best defense against most management plane attacks.

Monitor activity

Amazon provides three tools to monitor management activity within AWS. Enable all of them:

  • CloudTrail logs all management (API) activity on AWS services, including Amazon’s own connections to your assets. Where available it provides complete transparency for both your organization’s and Amazon’s access.
  • CloudWatch monitors the performance and utilization of your AWS assets, and ties tightly into billing. Set billing alarms to detect unusually high levels of activity. You can also send system logs to CloudWatch but this isn’t recommended as a security control.
  • Config is a new service that discovers services and configurations, and tracks changes over time. It is a much cleaner way to track configuration activity than CloudTrail.

CloudTrail and Config don’t cover all regions and services, so understand where the gaps are. As of this writing Config is still in preview, with minimal coverage, but both services expand capabilities regularly. These features provide important data feeds but most organizations use additional tools for overall collection and analysis, including log management and SIEM.

  • As a next step many organizations use a management portal (open source or commercial) instead of allowing direct access to AWS. This gives much tighter control over access and monitoring. Proxy administrator access with Privileged User Management, “jump boxes” or similar tools.
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