Cache Poisoning in Rails with Cockroachdb

Cache poisoning occurs when an attacker causes cached data to store malicious or incorrect values, leading to compromised responses for subsequent users. In a Ruby on Rails application using CockroachDB as the primary database, the risk arises from a combination of Rails caching behaviors and CockroachDB’s transactional and consistency characteristics.

Rails supports multiple cache stores, including memory, file store, and external stores such as Redis or Memcached. When caching is used to store query results that include tenant-specific or user-specific data, and the cache key does not incorporate sufficient context (e.g., tenant ID or user role), an attacker who can influence cache keys or cache content may cause sensitive data to be served to unauthorized users.

CockroachDB, being a distributed SQL database with strong consistency guarantees and serializable isolation, can affect how Rails applications handle caching strategies that rely on read-after-write consistency. For example, if Rails caches a database query result after a write transaction commits on CockroachDB, but the cache entry does not account for the specific execution context (such as the SQL session characteristics or the specific node topology), stale or incorrect data may persist in the cache. This is particularly relevant when using low-level cache APIs like Rails.cache.fetch with dynamic keys that omit tenant or scope identifiers.

Consider a scenario where an authenticated user can manipulate a query parameter that influences the cache key, such as params[:category], and the application uses this parameter to cache product listings stored in CockroachDB. If the cache key is built as "products/#{params[:category]}" without including the user ID or tenant ID, one user may receive cached data intended for another. CockroachDB’s long-lived serializable transactions do not inherently invalidate these caches, so poisoned entries can persist across commits.

Additionally, if the Rails app uses HTTP caching headers or fragment caching without properly scoping by security context, an attacker may leverage cross-user request patterns to poison shared cache entries. Because CockroachDB does not expose low-level cache management, the responsibility for correct cache scoping lies with the application logic in Rails.

To detect such issues, middleBrick scans the unauthenticated attack surface of Rails endpoints that interact with CockroachDB, checking for insufficient cache-key scoping, missing tenant context, and overly broad cache namespaces. Findings include references to the OWASP API Top 10 and guidance on how to align caching behavior with secure multi-tenant architectures.

Remediation focuses on ensuring cache keys incorporate all contextual identifiers that affect data visibility, including tenant or user scope, and avoiding reliance on cache entries that may mix data across security boundaries.

1. Include tenant and user identifiers in cache keys

Always build cache keys that include the tenant ID and user ID when caching data that is not globally shared. This prevents cross-tenant or cross-user cache poisoning.

# app/models/product.rb
class Product < ApplicationRecord
  def self.cached_list_for_tenant(tenant_id, user_id, category)
    Rails.cache.fetch(['products', tenant_id, user_id, category], expires_in: 12.hours) do
      where(tenant_id: tenant_id, category: category).to_a
    end
  end
end

2. Use low-level cache APIs with explicit namespacing

When using Rails.cache.fetch, ensure the key namespace reflects the data scope. Avoid generic keys like "top_products" in multi-tenant setups.

# app/controllers/products_controller.rb
def index
  @products = Rails.cache.fetch(['api', current_tenant.id, current_user.id, params[:category]], expires_in: 5.minutes) do
    current_tenant.products.where(category: params[:category]).limit(20).to_a
  end
  render json: @products
end

3. Avoid caching sensitive or user-specific data without scoping

Do not cache objects that contain PII or role-specific data unless the cache key includes the subject’s identifier. If caching is required, encrypt sensitive fields at rest and ensure the cache store supports encryption in transit.

# app/models/user_profile.rb
class UserProfile < ApplicationRecord
  def self.cached_for_user(user_id)
    Rails.cache.fetch(['user_profile', user_id], expires_in: 1.hour) do
      find_by(user_id: user_id)&.decorate
    end
  end
end

4. Coordinate cache expiration with CockroachDB transactions

When writes occur within serializable transactions, ensure cache expiration or invalidation happens within the same transactional context or via explicit callbacks to avoid stale reads caused by delayed cache updates.

# app/services/order_processor.rb
class OrderProcessor
  def self.execute(order_params)
    ApplicationRecord.transaction do
      order = Order.create!(order_params)
      Rails.cache.delete(['user_orders', order.user_id])
      order
    end
  end
end

5. Validate cache keys in middleware or before actions

Add a before action to verify that cache-derived data includes tenant context for controller actions that interact with CockroachDB-backed models.

# app/controllers/application_controller.rb
before_action :ensure_tenant_context_for_cacheable_actions

def ensure_tenant_context_for_cacheable_actions
  if params[:category] && !current_user&.tenant_id
    raise ActionController::BadRequest, 'Missing tenant context for cached resource'
  end
end

These practices reduce the risk of cache poisoning by ensuring cached responses are isolated per tenant and user. middleBrick can validate that your API endpoints correctly scope cached data and flag missing context before deployment.