Fantastic Infrastructure as Code security attacks and how to find them

Feb 17, 2022 · 24 min read · Leave a comment
Michael Friedrich GitLab profile

Infrastructure as Code(IaC) has eaten the world. It helps manage and provision computer resources automatically and avoids manual work or UI form workflows. Lifecycle management with IaC started with declarative and idempotent configuration, package, and tool installation. In the era of cloud providers, IaC tools additionally help abstract cloud provisioning. They can create defined resources automatically (network, storage, databases, etc.) and apply the configuration (DNS entries, firewall rules, etc.).

Like everything else, it has its flaws. IaC workflows have shifted left in the development lifecycle, making it more efficient. Developers and DevOps engineers need to learn new tools and best practices. Mistakes may result in leaked credentials or supply chain attacks. Existing security assessment tools might not be able to detect these new vulnerabilities.

In this post, we will dive into these specific risks and focus on IaC management tools such as Terraform, cloud providers, and deployment platforms involving containers and Kubernetes.

For each scenario, we will look into threats, tools, integrations, and best practices to reduce risk.

You can read the blog post top-down or navigate into the chapters individually.

Scan your infrastructure - know what is important

Start with identifying the project/group responsible for managing the IAC tasks. An inventory search for specific IaC tools, file suffixes (Terraform uses .tf, for example), and languages can be helpful. The security scan tools discussed in this blog post will discover all supported types automatically. Once you have identified the projects, you can use one of the tools to run a scan and identify the detected possible vulnerabilities.

There might not be any scan results because your infrastructure is secure at this time. Though, your processes may require you to create documentation, runbooks, and action items for eventually discovered vulnerabilities in the future. Creating a forecast on possible scenarios to defend is hard, so let us change roles from the defender to the attacker for a moment. Which security vulnerabilities are out there to exploit as a malicious attacker? Maybe it is possible to create vulnerable scenarios and simulate the attacker role by running a security scan.

Thinking like an attacker

There can be noticeable potential vulnerabilities like plaintext passwords in the configuration. Other scenarios involve cases you would never think of or a chain of items causing a security issue.

Let us create a scenario for an attacker by provisioning an S3 bucket in AWS with Terraform. We intend to store logs, database dumps, or credential vaults in this S3 bucket.

The following example creates the aws_s3_bucket resource in Terraform using the AWS provider.

# Create the bucket
resource "aws_s3_bucket" "demobucket" {
  bucket = "terraformdemobucket"
  acl = "private"
}

After provisioning the S3 bucket for the first time, someone decided to make the S3 bucket accessible by default. The example below grants public access to the bucket using aws_s3_bucket_public_access_block. block_public_acls and block_public_policy are set to false to allow any public access.

# Grant bucket access: public
resource "aws_s3_bucket_public_access_block" "publicaccess" {
  bucket = aws_s3_bucket.demobucket.id
  block_public_acls = false
  block_public_policy = false
}

The S3 bucket is now publicly readable, and anyone who knows the URL or scans network ranges for open ports may find the S3 bucket and its data. Malicious actors can not only capture credentials but also may learn about your infrastructure, IP addresses, internal server FQDNs, etc. from the logs, backups, and database dumps being stored in the S3 bucket.

We need ways to mitigate and detect this security problem. The following sections describe the different tools you can use. The full Terraform code is located in this project and allows you to test all tools described in this blog post.

Tools to detect Terraform vulnerabilities

In the "not worst case" scenario, the Terraform code to manage your infrastructure is persisted at a central Git server and not hidden somewhere on a host or local desktop. Maybe you are using terraform init, plan, apply jobs in CI/CD pipelines already. Let us look into methods and tools that help detect the public S3 bucket vulnerability. Later, we will discuss CI/CD integrations and automating IaC security scanning.

Before we dive into the tools, make sure to clone the demo project locally to follow the examples yourself.

$ cd /tmp
$ git clone https://gitlab.com/gitlab-de/use-cases/infrastructure-as-code-scanning.git && cd  infrastructure-as-code-scanning/

The tool installation steps in this blog post are illustrated with Homebrew on macOS. Please refer to the tools documentation for alternative installation methods and supported platforms.

You can follow the tools for Terraform security scanning by reading top-down, or navigate into the tools sections directly:

tfsec

tfsec from Aqua Security can help detect Terraform vulnerabilities. There are Docker images available to quickly test the scanner on the CLI, or binaries to install tfsec. Run tfsec on the local project path terraform/aws/ to get a list of vulnerabilities.

$ brew install tfsec
$ tfsec terraform/aws/

The default scan provides a table overview on the CLI, which may need additional filters. Inspect tfsec –help to get a list of all available parameters and try generating JSON and JUnit output files to process further.

$ tfsec terraform/aws --format json --out tfsec-report.json
1 file(s) written: tfsec-report.json
$ tfsec terraform/aws --format junit --out tfsec-junit.xml
1 file(s) written: tfsec-junit.xml

The full example is located in the terraform/aws directory in this project.

Parse tfsec JSON reports with jq

In an earlier blog post, we shared how to detect the JSON data structures and filter with chained jq commands. The tfsec report is a good practice: Extract the results key, iterate through all array list items and filtered by rule_service being s3, and only print severity, description and location.filename.

$ jq < tfsec-report.json | jq -c '.["results"]' | jq -c '.[] | select (.rule_service == "s3") | [.severity, .description, .location.filename]'

tfsec parser output example

kics

kics is another IaC scanner, providing support for many different tools (Ansible, Terraform, Kubernetes, Dockerfile, and cloud configuration APIs such as AWS CloudFormation, Azure Resource Manager, and Google Deployment Manager).

Let's try it: Install kics and run it on the vulnerable project. --report-formats, --output-path and --output-name allow you to create a JSON report which can be automatically parsed with additional tooling.

$ kics scan --path .
$ kics scan --path . --report-formats json --output-path kics --output-name kics-report.json

Parsing the JSON report from kics with jq works the same way as the tfsec example above. Inspect the data structure and nested object, and filter by AWS as cloud_provider. The files entry is an array of dictionaries, which turned out to be a little tricky to extract with an additional (.files[] | .file_name ) to add:

$ jq < kics/kics-report.json | jq -c '.["queries"]' | jq -c '.[] | select (.cloud_provider == "AWS") | [.severity, .description, (.files[] | .file_name ) ]'

kics json jq parser

kics returns different exit codes based on the number of different severities found. 50 indicates HIGH severities and causes your CI/CD pipeline to fail.

checkov

Checkov supports Terraform (for AWS, GCP, Azure and OCI), CloudFormation, ARM, Severless framework, Helm charts, Kubernetes, and Docker.

$ brew install checkov
$ checkov --directory .

terrascan

Terrascan supports Terraform, and more policies for cloud providers, Docker, and Kubernetes.

$ brew install terrascan
$ terrascan scan .

semgrep

Semgrep is working on Terraform support, currently in Beta. It also detects Dockerfile errors - for example invalid port ranges and multiple ranges, similar to kics.

$ brew install semgrep
$ semgrep --config auto .

tflint

tflint also is an alternative scanner.

Develop more IaC scenarios

While testing IaC Security Scanners for the first time, I was looking for demo projects and examples. The kics queries list for Terraform provides an exhaustive list of all vulnerabilities and the documentation linked. From there, you can build and create potential attack vectors for demos and showcases without leaking your company code and workflows.

Terragoat also is a great learning resource to test various scanners and see real-life examples for vulnerabilities.

$ cd /tmp && git clone https://github.com/bridgecrewio/terragoat.git && cd terragoat

$ tfsec .
$ kics scan --path .
$ checkov --directory .
$ semgrep --config auto .
$ terrascan scan .

It is also important to verify the reported vulnerabilities and create documentation for required actions for your teams. Not all detected vulnerabilities are necessarily equally critical in your environment. With the rapid development of IaC, GitOps, and cloud-native environments, it can also be a good idea to use 2+ scanners to see if there are missing vulnerabilities on one or the other.

The following sections discuss more scenarios in detail.

Terraform Module Dependency Scans

Re-usable IaC workflows also can introduce security vulnerabilities you are not aware of. This project provides the module files and package in the registry, which can be consumed by main.tf in the demo project.

module "my_module_name" {
  source = "gitlab.com/gitlab-de/iac-tf-vuln-module/aws"
  version = "1.0.0"
}

kics has limited support for the official Terraform module registry, checkov failed to download private modules, terrascan and tfsec work when terraform init is run before the scan. Depending on your requirements, running kics for everything and tfsec for module dependency checks can be a solution, suggestion added here.

IaC Security Scanning for Containers

Security problems in containers can lead to application deployment vulnerabilities. The kics query database helps to reverse engineer more vulnerable examples: Using the latest tag, privilege escalations with invoking sudo in a container, ports out of range, and multiple entrypoints are just a few bad practices.

The following Dockerfile implements example vulnerabilities for the scanners to detect:

# Create vulnerabilities based on kics queries in https://docs.kics.io/latest/queries/dockerfile-queries/
FROM debian:latest

# kics: Run Using Sudo
# kics: Run Using apt
RUN sudo apt install git

# kics: UNIX Ports Out Of Range
EXPOSE 99999

# kics: Multiple ENTRYPOINT Instructions Listed
ENTRYPOINT ["ex1"]
ENTRYPOINT ["ex2"]

Kics, tfsec, and terrascan can detect Dockerfile vulnerabilities, similar to semgrep and checkov. As an example scanner, terrascan can detect the vulnerabilities using the --iac-type docker parameter that allows to filter the scan type.

$ terrascan scan --iac-type docker

terrascan Docker IaC type scan result

You can run kics and tfsec as an exercise to verify the results.

IaC Security Scanning with Kubernetes

Securing a Kubernetes cluster can be a challenging task. Open Policy Agent, Kyverno, RBAC, etc., and many different YAML configuration attributes require reviews and automated checks before the production deployments. Cluster image scanning is one way to mitigate security threats, next to Container scanning for the applications being deployed. A suggested read is the book “Hacking Kubernetes” book by Andrew Martin and Michael Hausenblas if you want to dive deeper into Kubernetes security and attack vectors.

It's possible to make mistakes when, for example, copying YAML example configuration and continue using it. I've created a deployment and service for a Kubernetes monitoring workshop, which provides a practical example to learn but also uses some not so good practices.

The following configuration in ecc-demo-service.yml introduces vulnerabilities and potential production problems:

---
# A deployment for the ECC Prometheus demo service with 3 replicas.
apiVersion: apps/v1
kind: Deployment
metadata:
  name: ecc-demo-service
  labels:
    app: ecc-demo-service
spec:
  replicas: 3
  selector:
    matchLabels:
      app: ecc-demo-service
  template:
    metadata:
      labels:
        app: ecc-demo-service
    spec:
      containers:
      - name: ecc-demo-service
        image: registry.gitlab.com/everyonecancontribute/observability/prometheus_demo_service:latest
        imagePullPolicy: IfNotPresent
        args:
        - -listen-address=:80
        ports:
        - containerPort: 80
---
# A service that references the demo service deployment.
apiVersion: v1
kind: Service
metadata:
  name: ecc-demo-service
  labels:
    app: ecc-demo-service
spec:
  ports:
  - port: 80
    name: web
  selector:
    app: ecc-demo-service

Let's scan the Kubernetes manifest with kics and parse the results again with jq. A list of kics queries for Kubernetes can be found in the kics documentation.

$ kics scan --path kubernetes --report-formats json --output-path kics --output-name kics-report.json

$ jq < kics/kics-report.json | jq -c '.["queries"]' | jq -c '.[] | select (.platform == "Kubernetes") | [.severity, .description, (.files[] | .file_name ) ]'

Kubernetes manifest scans and jq parser results with kics

Checkov detects similar vulnerabilities with Kubernetes.

$ checkov --directory kubernetes/
$ checkov --directory kubernetes -o json > checkov-report.json

kube-linter analyzes Kubernetes YAML files and Helm charts for production readiness and security.

$ brew install kube-linter
$ kube-linter lint kubernetes/ecc-demo-service.yml --format json > kube-linter-report.json

kubesec provides security risk analysis for Kubernetes resources. kubesec is also integrated into the GitLab SAST scanners.

$ docker run -i kubesec/kubesec:512c5e0 scan /dev/stdin < kubernetes/ecc-demo-service.yml

Integrations into CI/CD and Merge Requests for Review

There are many scanners out there, and most of them return the results in JSON which can be parsed and integrated into your CI/CD pipelines. You can learn more about the evaluation of GitLab IaC scanners in this issue. The table in the issue includes licenses, languages, outputs, and examples.

checkov and tfsec provide JUnit XML reports as output format, which can be parsed and integrated into CI/CD. Vulnerability reports will need a different format though to not confuse them with unit test results for example. Integrating a SAST scanner in GitLab requires you to provide artifacts:reports:sast as a specified output format and API. This report can then be consumed by GitLab integrations such as MR widgets and vulnerability dashboards, available in the Ultimate tier. The following screenshot shows adding a Kubernetes deployment and service with potential vulnerabilities in this MR.

MR widget showing IaC vulnerabilities with Kubernetes

Reports in MRs as comment

There are different ways to collect the JSON reports in your CI/CD pipelines or scheduled runs. One of the ideas can be creating a merge request comment with a Markdown table. It needs a bit more work with parsing the reports, formatting the comment text, and interacting with the GitLab REST API, shown in the following steps in a Python script. You can follow the implementation steps to re-create them in your preferred language for the scanner type and use GitLab API clients.

First, read the report in JSON format, and inspect whether kics_version is set to continue. Then extract the queries key, and prepare the comment_body with the markdown table header columns.

FILE="kics/kics-report.json"

f = open(FILE)
report = json.load(f)

# Parse the report: kics
if "kics_version" in report:
    print("Found kics '%s' in '%s'" % (report["kics_version"], FILE))
    queries = report["queries"]
else:
    raise Exception("Unsupported report format")

comment_body = """### kics vulnerabilities report

| Severity | Description | Platform | Filename |
|----------|-------------|----------|----------|
"""

Next, we need to parse all queries in a loop, and collect all column values. They are collected into a new list, which then gets joined with the | character. The files key needs a nested collection, as this is a list of dictionaries where only the file_name is of interest for the demo.

# Example query to parse: {'query_name': 'Service Does Not Target Pod', 'query_id': '3ca03a61-3249-4c16-8427-6f8e47dda729', 'query_url': 'https://kubernetes.io/docs/concepts/services-networking/service/', 'severity': 'LOW', 'platform': 'Kubernetes', 'category': 'Insecure Configurations', 'description': 'Service should Target a Pod', 'description_id': 'e7c26645', 'files': [{'file_name': 'kubernetes/ecc-demo-service.yml', 'similarity_id': '9da6166956ad0fcfb1dd533df17852342dcbcca02ac559becaf51f6efdc015e8', 'line': 38, 'issue_type': 'IncorrectValue', 'search_key': 'metadata.name={{ecc-demo-service}}.spec.ports.name={{web}}.targetPort', 'search_line': 0, 'search_value': '', 'expected_value': 'metadata.name={{ecc-demo-service}}.spec.ports={{web}}.targetPort has a Pod Port', 'actual_value': 'metadata.name={{ecc-demo-service}}.spec.ports={{web}}.targetPort does not have a Pod Port'}]}

for q in queries:
    #print(q) # DEBUG
    l = []
    l.append(q["severity"])
    l.append(q["description"])
    l.append(q["platform"])

    if "files" in q:
        l.append(",".join((f["file_name"] for f in q["files"])))

    comment_body += "| " + " | ".join(l) + " |\n"

f.close()

The markdown table has been prepared, so now it is time to communicate with the GitLab API. python-gitlab provides a great abstraction layer with programmatic interfaces.

The GitLab API needs a project/group access token with API permissions. The CI_JOB_TOKEN is not sufficient.

Set the Project Access Token as CI/CD variable, not protected

Read the GITLAB_TOKEN from the environment, and instantiate a new Gitlab object.

GITLAB_URL='https://gitlab.com'

if 'GITLAB_TOKEN' in os.environ:
    gl = gitlab.Gitlab(GITLAB_URL, private_token=os.environ['GITLAB_TOKEN'])
else:
    raise Exception('GITLAB_TOKEN variable not set. Please provide an API token to update the MR!')

Next, use the CI_PROJECT_ID CI/CD variable from the environment to select the project object which contains the merge request we want to target.

project = gl.projects.get(os.environ['CI_PROJECT_ID'])

The tricky part is to fetch the merge request ID from the CI/CD pipeline, it is not always available. A workaround can be to read the CI_COMMIT_REF_NAME variable and match it against all MRs in the project, looking if the source_branch matches.

real_mr = None

if 'CI_MERGE_REQUEST_ID' in os.environ:
    mr_id = os.environ['CI_MERGE_REQUEST_ID']
    real_mr = project.mergerequests.get(mr_id)

# Note: This workaround can be very expensive in projects with many MRs
if 'CI_COMMIT_REF_NAME' in os.environ:
    commit_ref_name = os.environ['CI_COMMIT_REF_NAME']

    mrs = project.mergerequests.list()

    for mr in mrs:
        if mr.source_branch in commit_ref_name:
            real_mr = mr
            # found the MR for this source branch
            # print(mr) # DEBUG

if not real_mr:
    print("Pipeline not run in a merge request, no reports sent")
    sys.exit(0)

Last but not least, use the MR object to create a new note with the comment_body including the Markdown table created before.

mr_note = real_mr.notes.create({'body': comment_body})

This workflow creates a new MR comment every time a new commit is pushed. Consider evaluating the script and refining the update frequency by yourself. The script can be integrated into CI/CD with running kics before generating the reports shown in the following example configuration for .gitlab-ci.yml:

# Full RAW example for kics reports and scans
kics-scan:
  image: python:3.10.2-slim-bullseye
  variables:
    # Visit for new releases
    # https://github.com/Checkmarx/kics/releases
    KICS_VERSION: "1.5.1"
  script:
    - echo $CI_PIPELINE_SOURCE
    - echo $CI_COMMIT_REF_NAME
    - echo $CI_MERGE_REQUEST_ID
    - echo $CI_MERGE_REQUEST_IID
    - apt-get update && apt-get install wget tar --no-install-recommends
    - set -ex; wget -q -c "https://github.com/Checkmarx/kics/releases/download/v${KICS_VERSION}/kics_${KICS_VERSION}_linux_x64.tar.gz" -O - | tar -xz --directory /usr/bin &>/dev/null
    # local requirements
    - pip install -r requirements.txt
    - kics scan --no-progress -q /usr/bin/assets/queries -p $(pwd) -o $(pwd) --report-formats json --output-path kics --output-name kics-report.json || true
    - python ./integrations/kics-scan-report-mr-update.py

You can find the .gitlab-ci.yml configuration and the full script, including more inline comments and debug output in this project. You can see the implementation MR testing itself in this comment.

MR comment with the kics report as Markdown table

MR comments using GitLab IaC SAST reports as source

The steps in the previous section show the raw kics command execution, including JSON report parsing that requires you to create your own parsing logic. Alternatively, you can rely on the IaC scanner in GitLab and parse the SAST JSON report as a standardized format. This is available for all GitLab tiers.

Download the gl-sast-report.json example, save it as gl-sast-report.json in the same directory as the script, and parse the report in a similar way shown above.

FILE="gl-sast-report.json"

f = open(FILE)
report = json.load(f)

# Parse the report: kics
if "scan" in report:
    print("Found scanner '%s' in '%s'" % (report["scan"]["scanner"]["name"], FILE))
    queries = report["vulnerabilities"]
else:
    raise Exception("Unsupported report format")

The parameters in the vulnerability report also include the CVE number. The location is using a nested dictionary and thus easier to parse.

comment_body = """### IaC SAST vulnerabilities report

| Severity | Description | Category | Location | CVE |
|----------|-------------|----------|----------|-----|
"""

for q in queries:
    #print(q) # DEBUG
    l = []
    l.append(q["severity"])
    l.append(q["description"])
    l.append(q["category"])
    l.append(q["location"]["file"])
    l.append(q["cve"])

    comment_body += "| " + " | ".join(l) + " |\n"

f.close()

The comment_body contains the Markdown table, and can use the same code to update the MR with a comment using the GitLab API Python bindings. An example run is shown in this MR comment.

You can integrate the script into your CI/CD workflows using the following steps: 1) Override the kics-iac-sast job artifacts created by the Security/SAST-IaC.latest.gitlab-ci.yml template and 2) Add a job iac-sast-parse which parses the JSON report and calls the script to send a MR comment.

# GitLab integration with SAST reports spec
include:
- template: Security/SAST-IaC.latest.gitlab-ci.yml

# Override the SAST report artifacts
kics-iac-sast:
  artifacts:
    name: sast
    paths:
      - gl-sast-report.json
    reports:
      sast: gl-sast-report.json

iac-sast-parse:
  image: python:3.10.2-slim-bullseye
  needs: ['kics-iac-sast']
  script:
    - echo "Parsing gl-sast-report.json"
    - pip install -r requirements.txt
    - python ./integrations/sast-iac-report-mr-update.py
  artifacts:
      paths:
      - gl-sast-report.json

The CI/CD pipeline testing itself can be found in this MR comment. Please review the sast-iac-report-mr-update.py script and evaluate whether it is useful for your workflows.

What is the best integration strategy?

One way to evaluate the scanners is to look at their extensibility. For example, kics calls them queries, semgrep uses rules, checkov says policies, tfsec goes for custom checks as a name. These specifications allow you to create and contribute your own detection methods with extensive tutorial guides.

Many of the shown scanners provide container images to use, or CI/CD integration documentation. Make sure to include this requirement in your evaluation. For a fully integrated and tested solution, use the IaC Security Scanning feature in GitLab, currently based on the kics scanner. If you already have experience with other scanners, or prefer your own custom integration, evaluate the alternatives for your solution. All scanners discussed in this blog post provide JSON as output format, which helps with programmatic parsing and automation.

Maybe you'd like to contribute a new IaC scanner or help improve the detection rules and functionality from the open source scanners :-)

Cover image by Sawyer Bengtson on Unsplash

“Learn about possible attack scenarios in Infrastructure as Code and GitOps environments, evaluate tools and scanners with Terraform, Kubernetes, etc., and more.” – Michael Friedrich

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