Shellshock in Hanami with Dynamodb

Shellshock (CVE-2014-6271 and related variants) is a command injection vulnerability in the Bash shell that arises when untrusted data is passed to environment variables and then used in function definitions or exported values. In Hanami, a Ruby web framework that encourages explicit, object-oriented architecture, this typically surfaces when environment variables, HTTP headers, or user-controlled parameters are forwarded to system commands via system, exec, or backticks.

When Hanami applications interact with Amazon DynamoDB—either through the official AWS SDK or an abstraction layer—there is potential for Shellshock to be triggered if environment variables derived from attacker-controlled inputs are used in DynamoDB client configuration or in subprocess calls. For example, if a Hanami service builds environment variables for AWS credentials from request parameters and passes them to aws dynamodb CLI invocations, a malicious value containing Bash function exports can execute arbitrary code during SDK subprocess initialization. Even when using SDKs directly, indirect calls or system hooks that rely on Bash can be exploited if environment variables are not sanitized.

The risk is particularly acute when Hanami applications run in environments where Bash is invoked to manage DynamoDB-related tooling—such as custom scripts for table provisioning, backup workflows, or local emulation (e.g., aws dynamodb local). An attacker who can control an HTTP header like User-Agent or a request parameter that becomes part of an environment variable can craft payloads that execute commands, read files, or pivot within the infrastructure. Because DynamoDB operations often involve sensitive data, the impact of such injection can be severe, ranging from data exfiltration to lateral movement.

Using middleBrick’s LLM/AI Security checks and standard API scanning (the Authentication, Input Validation, and Unsafe Consumption checks apply here), you can detect whether your Hanami endpoints expose environment variables to Bash or whether DynamoDB-related tooling is invoked in a way that permits command injection. These scans do not fix the issue, but they highlight risky patterns in how environment variables and external commands are composed.

To mitigate Shellshock in Hanami when working with DynamoDB, ensure that no user-controlled data ever reaches Bash environment variables or subprocess arguments. Prefer the AWS SDK for Ruby (aws-sdk-dynamodb) over CLI invocations, and if CLI usage is unavoidable, sanitize and isolate the environment rigorously.

1. Use the AWS SDK directly, avoiding Bash

Replace any CLI-based DynamoDB calls with the official SDK, which does not invoke Bash. Configure credentials via trusted sources (IAM roles, instance profiles) rather than environment variables derived from requests.

# Good: Hanami service using aws-sdk-dynamodb directly
require 'aws-sdk-dynamodb'

class Hanami::Services::DynamoDbService
  def initialize
    @client = Aws::DynamoDB::Client.new(region: 'us-east-1')
  end

  def get_item(table_name, key)
    @client.get_item(table: table_name, key: key)
  end

  def put_item(table_name, item)
    @client.put_item(table: table_name, item: item)
  end
end

2. Avoid passing environment variables from user input

If you must use environment variables (for example, to set defaults), ensure they are set from trusted configuration files or deployment-time secrets, never from request parameters. Do not export attacker-controlled values into the environment that Bash may interpret.

# Bad: Setting env vars from params (risky)
ENV['AWS_ACCESS_KEY_ID'] = params[:access_key]

# Good: Use IAM roles or secure vaults instead
# No runtime ENV assignment from user input

3. Sanitize if using CLI invocations

If you must invoke aws dynamodb via system calls, use Open3.capture3 with explicit environment control and avoid inheriting the parent environment.

require 'open3'

env = { 'AWS_REGION' => 'us-east-1' }
command = ['aws', 'dynamodb', 'list-tables']
stdout, stderr, status = Open3.capture3(env, *command)

4. Validate and restrict inputs

Apply strict input validation on any data that could propagate into environment variables or command arguments. Combine this with middleBrick’s Input Validation and Property Authorization checks to enforce safe patterns.

# Example validation in a Hanami action
params.validate do
  required(:table_name).filled(:str?, format?: /\A[a-zA-Z0-9_-]+\z/)
end

5. Monitor and test with automated security scans

Use middleBrick’s GitHub Action to add API security checks to your CI/CD pipeline, failing builds if risk scores drop below your threshold. Run continuous monitoring on staging environments and leverage the Web Dashboard to track remediation progress over time.