Injection Flaws in Grape (Ruby)

Grape is a REST-like API micro-framework for Ruby. When building endpoints, developers compose routes and use parameters directly in queries, system commands, or serialization logic. If those parameters are concatenated into strings that are later interpreted by the shell, a database driver, or an OS command, injection becomes possible.

Because Grape encourages rapid endpoint definition, it is common to see string interpolation or concatenation with user input before a database query or a shell invocation. In Ruby, this often means using #{params[:id]} inside a string that is passed to an adapter, or building a command string for system, %x{...}, or exec. The interpreter treats the injected content as code or as part of a command, not as data.

For example, constructing a SQL query by joining strings with user input can lead to SQL injection, while passing unsanitized input to a shell command can lead to command injection. Similarly, unsafe deserialization of attacker-controlled data may lead to remote code execution. These flaws map to the Injection category in the OWASP API Top 10 and commonly appear in the BFLA/Privilege Escalation and Unsafe Consumption checks that middleBrick runs in parallel.

middleBrick tests the unauthenticated attack surface and, among its 12 security checks, looks for indicators of injection by analyzing request/response behavior and OpenAPI/Swagger specs (2.0, 3.0, 3.1) with full $ref resolution. It cross-references spec definitions with runtime findings to highlight risky parameter handling patterns without requiring authentication.

Real-world patterns include:

• Using string interpolation to build dynamic queries or commands.
• Passing raw JSON or form data directly to an eval-like construct or deserializer.
• Failing to parameterize queries or sanitize file paths used in system utilities.

Because Grape apps often sit behind a gateway and are consumed by many clients, injection flaws can have wide impact, exposing data or enabling unauthorized operations. Regular scanning with a tool that includes active checks — such as the LLM/AI Security probes and runtime behavior tests in middleBrick — helps detect these issues early in development.

Secure Ruby code in Grape avoids interpreting user input as code or as part of a command. Use parameterized queries, safe serialization APIs, and strict input validation to prevent injection.

SQL Injection Prevention

Use an ORM or a parameterized query interface. Do not interpolate parameters into SQL strings.

# Unsafe
get '/users/:search' do
  query = "SELECT * FROM users WHERE name = '#{params[:search]}'"
  DB[query].all
end

# Safe with Sequel (parameterized)
get '/users' do
  name = params[:name]
  DB[:users].where(name: name).all
end

# Safe with ActiveRecord (parameterized)
get '/users' do
  name = params[:name]
  User.where(name: name).to_a
end

Command Injection Prevention

Do not build shell commands with string interpolation. Use argument arrays and avoid shell metacharacters.

# Unsafe
get '/ping' do
  host = params[:host]
  %x{ping -c 1 #{host}}
end

# Safe with explicit arguments
get '/ping' do
  host = params[:host]
  # system with separate arguments; shell is not used
  system('ping', '-c', '1', host)
end

Deserialization and Eval Safeguards

Avoid eval, instance_eval, or unsafe YAML/Marshal deserialization of untrusted data.

# Unsafe
post '/run' do
  code = params[:script]
  eval(code)
end

# Safe: strict input schema validation + no eval
post '/run' do
  # Validate and parse expected structure; do not execute code
  halt 400, { error: 'Unsupported operation' }.to_json
end

Path Traversal and File Inclusion

Sanitize file paths and avoid direct concatenation with user input.

# Unsafe
get '/files/:name' do
  path = "/var/data/#{params[:name]}"
  File.read(path)
end

# Safe: restrict to a base directory and validate filename
require 'pathname'
BASE = Pathname.new('/var/data').expand_path
get '/files/:name' do
  requested = Pathname.new(params[:name]).cleanpath
  full = BASE.join(requested).cleanpath
  halt 400 unless full.to_path.start_with?(BASE.to_path)
  File.read(full)
end

Input Validation and Type Coercion

Use strong parameters and type checks; reject unexpected formats early.

# Example with a simple schema check
helpers do
  def permitted_params
    declared_params = params.permit(:id, :query, :format)
    declared_params[:id] = Integer(declared_params[:id]) rescue nil
    declared_params[:query] = String(declared_params[:query]).strip
    declared_params
  end
end

get '/items' do
  p = permitted_params
  # Use p[:id] and p[:query] safely as integers/strings
  { id: p[:id], query: p[:query] }.to_json
end