attack-surface.md

Attack Surface Analysis for ryanb/cancan

Attack Surface: 1. Overly Permissive Authorization Rules

• Description: Rules defined in the Ability class grant broader access than intended, allowing users to perform actions they should not be authorized to do. This is the core vulnerability related to CanCan misuse.
• How CanCan Contributes: CanCan's declarative rule system, while powerful, can be misused to create overly broad permissions if not carefully designed and reviewed. The flexibility of the can :manage, :all syntax and complex conditions can lead to errors. This is inherent to how CanCan operates.
• Example: A rule intended for administrators (can :manage, User) is accidentally applied to all logged-in users due to a missing condition or a typo in the role check. Or, can :read, Article, published: true might have a flaw in how published is determined, leading to unauthorized access to draft articles.
• Impact: Unauthorized data access, modification, or deletion. Privilege escalation, allowing regular users to perform administrative actions. Complete system compromise in extreme cases.
• Risk Severity: Critical
• Mitigation Strategies:
  • Principle of Least Privilege: Start by denying all access (cannot :manage, :all). Explicitly grant only the minimum necessary permissions.
  • Granular Rules: Define highly specific rules. Avoid broad can :manage statements. Use specific actions (e.g., :create, :read, :update, :destroy).
  • Mandatory Code Reviews: Require at least two experienced developers to review every change to the Ability class.
  • Comprehensive Test Suite: Develop a comprehensive suite of unit and integration tests targeting authorization. Test positive and negative cases for every rule and condition.
  • Regular Security Audits: Conduct periodic security audits of the authorization logic.
  • Use cannot for Default Deny: Explicitly use cannot to deny actions, creating a "default deny" approach.

Attack Surface: 2. Flawed Condition Logic

• Description: Conditions within can blocks (e.g., can :update, Article, user_id: user.id) contain errors, leading to incorrect authorization decisions. This directly relates to how CanCan evaluates conditions.
• How CanCan Contributes: CanCan allows for complex conditions, including Ruby code and database queries within its authorization logic. This flexibility increases the risk of introducing logic errors or vulnerabilities within the CanCan rules themselves.
• Example: A condition checking for ownership (user_id: user.id) might be bypassed if the user_id field can be manipulated. A condition relying on a complex SQL query might have an injection vulnerability (if not using parameterized queries).
• Impact: Unauthorized access to resources, potentially allowing users to modify or delete data they don't own. Bypass of intended authorization restrictions.
• Risk Severity: High
• Mitigation Strategies:
  • Simplify Conditions: Keep conditions as simple as possible. Avoid complex logic or nested conditions.
  • Input Validation and Sanitization: Always validate and sanitize data used within CanCan conditions.
  • Parameterized Queries (or ORM Equivalent): Always use parameterized queries (or the ORM equivalent) for database queries within CanCan conditions to prevent SQL injection.
  • Thorough Testing of Conditions: Test conditions with a wide range of inputs, including edge cases and invalid data.
  • Avoid Direct Use of params: Minimize direct use of params within conditions.

Attack Surface: 3. Missing Authorization Checks

• Description: Developers forget to use load_and_authorize_resource (or authorize_resource) in controller actions, bypassing CanCan's checks entirely. This is a direct failure to utilize CanCan's core functionality.
• How CanCan Contributes: CanCan relies on developers to explicitly invoke authorization checks using its provided methods. Omitting these calls means CanCan is not being used for authorization, which is a direct misuse of the gem.
• Example: A controller action that directly accesses the database without calling load_and_authorize_resource will not have any CanCan authorization applied.
• Impact: Complete bypass of authorization, allowing unauthorized users to access and modify any data.
• Risk Severity: Critical
• Mitigation Strategies:
  • Enforce Consistent Usage: Require load_and_authorize_resource (or authorize_resource) in every controller action requiring authorization.
  • Automated Checks: Use static analysis tools or linters to detect missing authorization checks.
  • Controller-Level check_authorization: Use check_authorization in your ApplicationController to raise an exception if authorization is not checked.
  • Code Reviews: Code reviews should always check for the presence of authorization checks.
  • Training and Awareness: Ensure all developers are thoroughly trained on CanCan.

Attack Surface: 4. Bypassing accessible_by

• Description: Developers construct custom database queries instead of using CanCan's accessible_by method, circumventing CanCan's query scoping and potentially exposing unauthorized data. This is a direct avoidance of a key CanCan security feature.
• How CanCan Contributes: accessible_by is a core CanCan feature designed to automatically scope queries based on the defined authorization rules. Bypassing it directly undermines CanCan's security model.
• Example: Instead of @articles = Article.accessible_by(current_ability), a developer writes a custom query that doesn't respect the authorization rules.
• Impact: Unauthorized data disclosure. Users might view data they shouldn't have access to.
• Risk Severity: High
• Mitigation Strategies:
  • Enforce accessible_by Usage: Mandate or strongly encourage the use of accessible_by for all queries retrieving collections of resources.
  • Code Reviews: Flag any custom queries that might bypass authorization.
  • Training: Ensure developers understand the purpose and importance of accessible_by.
  • Alternative Query Builders: If complex queries are needed, consider using a dedicated query builder class that still uses accessible_by as its foundation.