Broken Authentication in Rails with Dynamodb

Broken Authentication in a Ruby on Rails application using Amazon DynamoDB as the primary data store often stems from mismatches between Rails’ session and credential management patterns and the eventual, schema-less nature of DynamoDB. When authentication logic assumes strong relational constraints or transactional rollbacks, insecure defaults can be introduced.

One common pattern is storing user credentials or session tokens directly in a DynamoDB table without sufficient protection. For example, if the Rails app uses the aws-sdk-dynamodb client to write an authentication token into a table and omits server-side encryption or fine-grained IAM policies, an attacker who can read that table may hijack sessions. The lack of built-in row-level security in DynamoDB means access controls must be enforced at the application layer, and if Rails does not consistently apply them, IDOR or BOLA issues emerge.

Another vulnerability vector is weak credential validation that does not align with DynamoDB’s primary-key design. If the partition key for the users table is a user ID derived from an unverified parameter, an attacker can enumerate identifiers and probe for valid accounts without triggering account lockouts. Rails’ default session store may also rely on cookie-based session IDs; if those IDs are predictable or not bound to the DynamoDB-stored user context, an attacker can fixate or steal sessions.

Additionally, DynamoDB’s lack of native joins or referential integrity can lead to incomplete authorization checks. A Rails controller might query DynamoDB for a user object and then assume a role or scope embedded in that object without re-validating the token’s scope for the requested action. This can enable privilege escalation when horizontal access controls are not rechecked on each request, a pattern highlighted in the BOLA/IDOR checks of middleBrick’s scans.

Lastly, unauthenticated exposure of authentication endpoints can occur if Rails routes for password reset or token verification are not properly constrained. middleBrick’s Authentication and BOLA/IDOR checks look for these exposures by correlating the OpenAPI spec (including any $ref-resolved definitions for securitySchemes) with runtime behavior, identifying gaps where authentication should be enforced but isn’t.

Remediation focuses on ensuring that authentication state is stored and accessed securely within DynamoDB’s model, with strict application-level checks and hardened Rails configuration.

Secure user table design and access patterns

Define a DynamoDB table with a composite key that avoids predictable enumeration. Use a UUID for the partition key and a sort key for secondary attributes if needed. Enforce encryption at rest using AWS KMS and apply least-privilege IAM policies scoped to specific actions and conditional expressions.

Example: Secure user creation and authentication with conditional writes

require 'aws-sdk-dynamodb'

class UserRepository
  def initialize
    @dynamodb = Aws::DynamoDB::Client.new(region: 'us-east-1')
    @table_name = ENV.fetch('DYNAMODB_USERS_TABLE')
  end

  # Create user with a condition to avoid overwriting an existing account
  def create_user(email:, password_hash:, uuid:)
    @dynamodb.put_item(
      table_name: @table_name,
      item: {
        user_id: { s: uuid },
        email: { s: email },
        password_hash: { s: password_hash },
        created_at: { n: Time.now.utc.to_i.to_s }
      },
      condition_expression: 'attribute_not_exists(user_id)'
    )
  rescue Aws::DynamoDB::Errors::ConditionalCheckFailedException
    raise 'User already exists'
  end

  # Retrieve user by partition key only, avoiding scans
  def find_user_by_id(user_id)
    resp = @dynamodb.get_item(
      table_name: @table_name,
      key: {
        user_id: { s: user_id }
      }
    )
    resp.item
  end
end

Example: Session/token storage with ownership binding

Store session tokens with a composite key that binds the token to the user_id, and include metadata for revocation checks. Always verify the token against the user record before elevating privileges.

class SessionRepository
  def initialize
    @dynamodb = Aws::DynamoDB::Client.new(region: 'us-east-1')
    @table_name = ENV.fetch('DYNAMODB_SESSIONS_TABLE')
  end

  def create_session(user_id:, token:, expires_at:)
    @dynamodb.put_item(
      table_name: @table_name,
      item: {
        token_id: { s: token },
        user_id: { s: user_id },
        expires_at: { n: expires_at.to_i.to_s },
        created_at: { n: Time.now.utc.to_i.to_s }
      },
      condition_expression: 'attribute_not_exists(token_id)'
    )
  end

  def find_session(token)
    resp = @dynamodb.get_item(
      table_name: @table_name,
      key: {
        token_id: { s: token }
      }
    )
    resp.item
  end

  def revoke_session(token)
    @dynamodb.delete_item(
      table_name: @table_name,
      key: {
        token_id: { s: token }
      }
    )
  end
end

Rails controller checks and binding to DynamoDB records

In controllers, always reload the user from DynamoDB using the canonical user_id from the token or session, and re-validate permissions per request. Avoid relying on cached attributes that may not reflect the latest security state.

class ApiController < ApplicationController
  before_action :authenticate_user!

  def sensitive_action
    user = UserRepository.new.find_user_by_id(current_user_id)
    raise 'Unauthorized' unless user && user['email'] == permitted_email?

    # proceed with DynamoDB-bound authorization
  end

  private

  def current_user_id
    # extract from token/session with DynamoDB-backed validation
  end

  def authenticate_user!
    # ensure token exists in DynamoDB and is not expired/revoked
  end
end

Additional hardening

• Use parameterized queries and condition expressions to prevent injection and race conditions.
• Enable DynamoDB Streams with secure processing if you need audit trails, but do not rely on them for real-time access control.
• Apply rate limiting and suspicious activity detection at the Rails layer, complementing DynamoDB’s lack of native throttling on individual items.
• Validate and encode all outputs to prevent injection into downstream consumers, addressing input validation and data exposure checks highlighted by middleBrick’s scans.