Terraform scanning with Snyk IaC doesn’t just find misconfigurations; it reveals the underlying assumptions your infrastructure code is making about your cloud provider’s security posture.
Let’s watch Snyk IaC in action. Imagine you have a Terraform file for an AWS S3 bucket.
resource "aws_s3_bucket" "my_secure_bucket" {
bucket = "my-truly-secure-bucket-12345"
acl = "private" # This looks good, right?
tags = {
Environment = "Production"
}
}
resource "aws_s3_bucket_public_access_block" "my_secure_bucket_block" {
bucket = aws_s3_bucket.my_secure_bucket.id
block_public_acls = true
block_public_policy = true
ignore_public_acls = true
restrict_public_buckets = true
}
You run snyk iac test. Snyk might report:
Testing tf/main.tf...
[SNYK-CC-TF-1] **High** Publicly Accessible S3 Bucket
Resource: aws_s3_bucket.my_secure_bucket
.acl: "private" is not sufficient to prevent public access.
See: https://docs.s3.amazonaws.com/aws-sdk-ddb/latest/APIReference/API_CreateBucket.html
Remediation: Set the 'acl' argument to 'private' and ensure no public policies are attached.
This output is useful, but it doesn’t tell the whole story. The acl = "private" setting on its own is often insufficient because other AWS configurations, like bucket policies or IAM policies, can still grant public access. Snyk’s Publicly Accessible S3 Bucket check (often SNYK-CC-TF-1) is looking for this broader context. It’s not just about the direct acl attribute; it’s about the effective access.
The problem Snyk IaC solves is the inherent difficulty in reasoning about the aggregate security state of cloud infrastructure defined by code. Manually auditing complex Terraform or CloudFormation for every potential security hole is error-prone and time-consuming. Snyk IaC automates this by understanding the semantics of these configuration languages and mapping them to known security vulnerabilities and best practices.
Internally, Snyk IaC parses your infrastructure-as-code files into an Abstract Syntax Tree (AST). It then applies a vast library of built-in rules, often derived from CIS Benchmarks, OWASP Top 10, and other industry standards, to this AST. These rules are designed to detect specific insecure patterns, missing security controls, or overly permissive configurations. For example, a rule might check if an EC2 instance is launched without a public IP address, or if a security group allows SSH access from 0.0.0.0/0. The output you see is the result of these rules matching patterns in your AST.
The levers you control are primarily within your Terraform or CloudFormation code. You fix issues by modifying resource attributes. For instance, to address the S3 bucket example, you might remove the acl attribute entirely and rely solely on the aws_s3_bucket_public_access_block resource, which is the more modern and recommended approach for blocking public access.
resource "aws_s3_bucket" "my_secure_bucket" {
bucket = "my-truly-secure-bucket-12345"
# acl attribute removed, relying on Public Access Block
tags = {
Environment = "Production"
}
}
resource "aws_s3_bucket_public_access_block" "my_secure_bucket_block" {
bucket = aws_s3_bucket.my_secure_bucket.id
block_public_acls = true
block_public_policy = true
ignore_public_acls = true
restrict_public_buckets = true
}
When Snyk scans this again, the Publicly Accessible S3 Bucket finding should be gone because the Public Access Block is now the definitive control.
A subtle but critical aspect of Snyk IaC’s effectiveness is its understanding of resource dependencies and attribute interpolation. It doesn’t just look at individual resource blocks in isolation. If your Terraform code references variables or outputs from other resources, Snyk attempts to resolve these references to understand the effective configuration. For instance, if an EC2 instance’s security group is defined using a variable that is itself set to allow broad access, Snyk can trace this back. This allows it to detect issues that might only become apparent when multiple, seemingly innocuous configurations are combined. This dependency analysis is key to finding complex, multi-resource misconfigurations that simple linters would miss.
The next concept you’ll likely encounter is managing custom IaC rules, allowing you to enforce your organization’s specific security policies beyond the built-in checks.