Network Infrastructure Automation (NIA) overview

Network Infrastructure Automation (NIA) enables dynamic updates to network infrastructure devices triggered by service changes using the Consul Terraform Sync (consul-terraform-sync) daemon. This daemon uses Consul's catalog to monitor networking information about services along with Terraform's provider ecosystem to apply relevant changes to network infrastructure.

The Secure Consul-Terraform-Sync for Production tutorial contains a checklist of best practices to secure your Consul-Terraform-Sync installation for a production environment.

Personas

When considering Consul NIA's security model, it helps to think of the following personas.

System Administrator - This is someone who has access to the underlying infrastructure of the NIA daemon (consul-terraform-sync), and possibly the core Consul service. Often she has access to SSH directly into a server within a cluster through a bastion host. Ultimately they have read, write, and execute permissions for the consul-terraform-sync binary. These users potentially have sudo, administrative, or some other privileged access to the underlying compute resource. Users like these are essentially totally trusted by NIA as they have administrative rights to the system.
Consul NIA Operator - This is someone who has access to define the consul-terraform-sync configuration, and possibly a Consul ACL token, and other secrets used to interact with various network infrastructure APIs. They have full access to all parts of consul-terraform-sync including the ability to configure, start, and stop the daemon.
Developer - This is someone who is responsible for creating, and possibly deploying applications connected, or configured with Consul. In some cases they may have no access, or limited capabilities to view Consul information, such as through metrics, or logs.
User - The end-user using the applications and other services managed by the NIA daemon, and should have no knowledge or access to the daemon's API endpoints, ACL tokens, certificates, or any other piece of the system.

Secure Configuration

Consul NIA's security model is applicable only if all parts of the system are running with a secure configuration; consul-terraform-sync is not secure-by-default. Without the following mechanisms enabled in the daemon's configuration, it may be possible to abuse access to the daemon. Like all security considerations, one must determine what concerns are appropriate for their environment, and adapt these security concerns accordingly.

Requirements

Protect Configuration Files and Directories - A dedicated NIA user and group with limited permissions should be created for production, along with directory, and file permissions appropriately scoped for your operating environment.
Example commands to illustrate creating a dedicated consul-nia system user, along with the supporting directories, configuration file, and securing those permissions using chown and chmod:
```
$ useradd --system --shell /bin/false consul-nia
$ mkdir -p /consul-nia/data
$ mkdir -p /consul-nia/config
$ echo "{ ... }" > /consul-nia/config/file.hcl
$ chown --recursive consul-nia:consul-nia /consul-nia
$ chmod -R 0750 consul-nia/
```
Protect Consul KV Path or Namespaces - Note the daemon can monitor Consul services in other Namespaces. This can be limited based on the ACL token used for the daemon.
Use Consul ACLs - The Access Control List (ACL) system within Consul can be used to restrict access to only the required parts of Consul for the NIA daemon to operate.
- Read + Write permission for Consul KV to the specified path, and namespace.
- Read permission for Consul Catalog for all of the selected services to be monitored, and their namespaces.
- Read + Write permission to update health checks, when using NIA health monitoring.

Recommendations

Use Dedicated Host - The NIA daemon will potentially have access to critical secrets for your environment's network infrastructure. Using a hardened, dedicated host, for supporting these sensitive operations is highly recommended.
Run without Root - The NIA daemon does not require root or other administrative privileges to operate.
Protect NIA Daemon API Endpoint - Any network endpoints provided by, or exposed to the NIA Daemon should be protected using Consul service mesh and appropriate firewall rules.
Use a centralized logging solution - Export log entries within syslog generated from consul-terraform-sync to a centralized logging solution.
Audit used Terraform providers - Terraform providers that are configured with the NIA daemon should be audited to ensure you're only using providers from sources that you trust.

Threat Model

The following are the parts of the NIA threat model:

Consul agent communication - In order to monitor the Consul Catalog for changes, the NIA daemon interacts with Consul's HTTP API on a local or remote server agent. This communication requires TLS transport encryption, preferably using mTLS for mutual authentication.
NIA Terraform communication - Network connectivity to downstream infrastructure APIs managed by the NIA daemon's Terraform runs will need to be properly configured for secure access.
Tampering of data in transit - Any tampering should be detectable and cause the daemon to avoid processing the request.
Access to data without authentication or authorization - Requests to the Consul agent should be authenticated and authorized using (m)TLS and ACLs respectively. ACLs should be configured with the minimal permissions required for your environment.
Denial-of-Service - DoS attacks against the NIA Daemon should not compromise the security of Consul, or Terraform, but may impact any networking components relying on updates from the daemon to properly handle traffic within the network. Access to the daemon should be prevented using firewall rules.

The following are not a part of the threat model, as the NIA Daemon expects a secure configuration, while always providing the default options for testing in local environments which cannot be automatically configured to be both secure, and easily usable. However, these are valid concerns for Administrators and Operators to evaluate when hardening a production deployment:

Access (read or write) to the Consul NIA Configuration Files or Directory - Necessary configuration for the daemon process can be loaded from a single file or a directory of files. These configurations may contain secrets and can enable/disable insecure features, or Terraform providers.
Access (read or write) to the Consul NIA Consul KV Path - Access to the daemon's Consul KV path may leak sensitive information such as usernames, passwords, certificates, and tokens used by Terraform to provision infrastructure.
Memory Access to a Running Consul-Terraform-Sync Process - Direct access to the memory of running the daemon process allows an attacker to extract sensitive information.
Memory Access to a Running Terraform Process - Direct access to the memory of running the Terraform process managed by the daemon process allows an attacker to extract sensitive information.
Access to the Terraform Binary - Direct access to the Terraform binary used by the NIA daemon can allow an attacker to extract sensitive information.
Access to the Consul-Terraform-Sync Binary - Direct access to the system binary used to start the NIA daemon can allow an attacker to extract sensitive information.

Internal Threats

NIA Operator - Someone with access to the NIA Host, and it's related binaries or configuration files may be a threat to your deployment, especially considering multi-team deployments. They may accidentally or intentionally use a malicious Terraform provider, or extract various secrets to cause harm to the network. Access to the NIA host should be guarded.
Consul Operator - Someone with access to the backend Consul cluster, similar to the NIA Operator, which can perform actions that may trigger Terraform runs. They may also have access to the namespace and KV path of the NIA daemon, which could give unintended access to Terraform's state file, which contains sensitive information. ACL permissions for Consul should be carefully audited to ensure that no policies may be leaking the state file containing sensitive information to other Consul operators unintentionally within the cluster.
System-bound Attackers - Multi-tenant environments, especially container orchestrators, can introduce a number of security concerns. These may include shared secrets, host volume access, and other sources of potential pivoting, or privilege escalation from attackers with operating system-level access, or side-car container access, through various means. Extra steps to configuring OS, cluster, service, user, directory, and file permissions are essential steps for implementing defense-in-depth within a production environment.

External Threats

Terraform Providers and Modules - Potentially malicious providers or modules, or any malicious dependencies part of the Terraform ecosystem could cause harm to the network, and may have access to secrets in order to make necessary network changes. Terraform provider configuration should be audited, pinned to a version, and audited for potential typo-squatting issues from the Terraform Registry.
Network-bound Attackers - Whenever a service is exposed to the open internet, which may be the case, you really need to consider external network attackers which may seek-out hidden, unauthenticated, or otherwise vulnerable endpoints. This can lead to larger security concerns when able to pivot to internal resources from an external one.
Leaking Secrets - TLS certificates and tokens used by the Consul NIA daemon can enable external attackers to access Consul, or Terraform resources. These secrets shouldn't be hardcoded into configs uploaded to public places like GitHub.