Operating models for Web App Security Governance in AWS

For most organizations, protecting their high value assets is a top priority. AWS Web Application Firewall (AWS WAF) is an industry leading solution that protects web applications from the evolving threat landscape, which includes common web exploits and bots. These threats affect availability, compromise security, or can consume excessive resources. Though AWS WAF is a managed service, the operating model of this critical first layer of defence is often overlooked.

Operating models for a core service like AWS WAF differ depending on your company’s technology footprint, and use cases are dependent on workloads. While some businesses were born in the public cloud and have modern applications, many large established businesses have classic and legacy workloads across their business units. We will examine three distinct operating models using AWS WAF, AWS Firewall Manager service (AWS FMS), AWS Organizations, and other AWS services.

Operating Models

I. Centralized

The centralized model works well for organizations where the applications to be protected by AWS WAF are similar, and rules can be consistent. With multi-tenant environments (where tenants share the same infrastructure or application), AWS WAF can be deployed with the same web access control lists (web ACLs) and rules for consistent security. Content management systems (CMS) also benefit from this model, since consistent web ACL and rules can protect multiple websites hosted on their CMS platform. This operating model provides uniform protection against web-based attacks and centralized administration across multiple AWS accounts. For managing all your accounts and applications in AWS Organizations, use AWS Firewall Manager.

AWS Firewall Manager simplifies your AWS WAF administration and helps you enforce AWS WAF rules on the resources in all accounts in an AWS Organization, by using AWS Config in the background. The compliance dashboard gives you a simplified view of the security posture. A centralized information security (IS) team can configure and manage AWS WAF’s managed and custom rules.

AWS Managed Rules are designed to protect against common web threats, providing an additional layer of security for your applications. By leveraging AWS Managed Rules and their pre-configured rule groups, you can streamline the management of WAF configurations. This reduces the need for specialized teams to handle these complex tasks and thereby alleviates undifferentiated heavy lifting.

A centralized operating pattern (see Figure 1) requires IS teams to construct an AWS WAF policy by using AWS FMS and then implement it at scale in each and every account. Keeping current on the constantly changing threat landscape can be time-consuming and expensive. Security teams will have the option of selecting one or more rule groups from AWS Managed Rules or an AWS Marketplace subscription for each web ACL, along with any custom rule needed.

Figure 1. Centralized operating model for AWS WAF

AWS Config managed rule sets ensure AWS WAF logging, rule groups, web ACLs, and regional and global AWS WAF deployments have no empty rule sets. Managed rule sets simplify compliance monitoring and reporting, while assuring security and compliance. AWS CloudTrail monitors changes to AWS WAF configurations, providing valuable auditing capability of your operating environment.

This model places the responsibility for defining, enforcing, and reviewing security policies, as well as remediating any issues, squarely on the security administrator and IS team. While comprehensive, this approach may require careful management to avoid potential bottlenecks, especially in larger-scale operations.

II. Distributed

Many organizations start their IT operations on AWS from their inception. These organizations typically have multi-skilled infrastructure and development teams and a lean operating model. The distributed model shown in Figure 2 is a good fit for them. In this case, the application team understands the underlying infrastructure components and the Infrastructure as Code (IaC) that provisions them. It makes sense for these development teams to also manage the interconnected application security components, like AWS WAF.

The application teams own the deployment of AWS WAF and the setup of the Web ACLs for their respective applications. Typically, the Web ACL will be a combination of baseline rule groups and use case specific rule groups, both deployed and managed by the application team.

One of the challenges that comes with the distributed deployment is the inconsistency in rules’ deployment which can result in varying levels of protection. Conflicting priorities within application teams can sometimes compromise the focus on security, prioritizing feature rollouts over comprehensive risk mitigation, for example. A strong governance model can be very helpful in situations like these, where the security team might not be responsible for deploying the AWS WAF rules, but do need security posture visibility. AWS Security services like Security Hub and Config rules can help set these parameters. For example, some of the managed Config rules and Security Hub controls check if AWS WAF is enabled for Application Load Balancer (ALB) and Amazon API Gateway, and also if the associated Web ACL is empty.

Figure 2. Distributed operating model for AWS WAF

III. Hybrid

An organization that has a diverse range of customer-facing applications hosted in a number of different AWS accounts can benefit from a hybrid deployment operating model. Organizations whose infrastructure is managed by a combination of an in-house security team, third-party vendors, contractors, and a managed cybersecurity operations center (CSOC) can also use this model. In this case, the security team can build and enforce a core AWS WAF rule set using AWS Firewall Manager. Application teams, can build and manage additional rules based on the requirements of the application. For example, use case specific rule groups will be different for PHP applications as compared to WordPress-based applications.

Information security teams can specify how core rule groups are ordered. The application administrator has the ability to add rules and rule groups that will be executed between the two rule group sets. This approach ensures that adequate security is applied to all legacy and modern applications, and developers can still write and manage custom rules for enhanced protection.

Organizations should adopt a collaborative DevSecOps model of development, where both the security team and the application development teams will build, manage, and deploy security rules. This can also be considered a hybrid approach combining the best of the central and distributed models, as shown in Figure 3.

Figure 3. Hybrid operating model for AWS WAF

Governance is shared between the centralized security team responsible for baseline rules sets deployed across all AWS accounts, and the individual application team responsible for AWS WAF custom rule sets. To maintain security and compliance, AWS Config checks Amazon CloudFront, AWS AppSync, Amazon API Gateway, and ALB for AWS WAF association with managed rule sets. AWS Security Hub combines and prioritizes AWS Firewall Manager security findings, enabling visibility into AWS WAF rule conformance across AWS accounts and resources. This model requires close coordination between the two teams to ensure that security policies are consistent and all security issues are effectively addressed.

The AWS WAF incident response strategy includes detecting, investigating, containing, and documenting incidents, alerting personnel, developing response plans, implementing mitigation measures, and continuous improvement based on lessons learned. Threat modelling for AWS WAF involves identifying assets, assessing threats and vulnerabilities, defining security controls, testing and monitoring, and staying updated on threats and AWS WAF updates.

Conclusion

Using the appropriate operating model is key to ensuring that the right web application security controls are implemented. It accounts for the needs of both business and application owners. In the majority of implementations, the centralized and hybrid model works well, by providing a stratified policy enforcement. However, the distributed method can be used to manage specific use cases. Amazon Firewall Manager services can be used to streamline the management of centralized and hybrid operating models across AWS Organizations.