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Attack Tree Analysis for rails-api/active_model_serializers

Objective: Exfiltrate sensitive data (e.g., user credentials, private messages, internal IDs) by exploiting overly permissive attribute inclusion or relationship handling in active_model_serializers configurations.

Attack Tree Visualization

                                      Compromise Application via AMS
                                                  |
                                         1. Data Leakage [CRITICAL]
                                                  |
                                  -----------------------------
                                  |
                            1.1 [HIGH] [CRITICAL]        1.2 [HIGH] [CRITICAL]
                            Inclusion of                 Attribute Exposure
                            Sensitive Data               (via relationships)
                            [CRITICAL]                   [CRITICAL]
                                        ^
                                        |
                                        |
                                  ---------------
                                  |
                            3.1 [HIGH]
                            Overly Permissive
                            Attribute Inclusion
                            (Default or Explicit)

Attack Tree Path: 1. Data Leakage [CRITICAL]

  • Overall Description: This is the root of the high-risk sub-tree. The primary vulnerability associated with active_model_serializers is the unintentional exposure of sensitive data through the API.
  • Why it's Critical: Successful exploitation directly achieves the attacker's goal of data exfiltration.
  • Why it's High-Risk: It encompasses the most common and easily exploitable vulnerabilities.

Attack Tree Path: 1.1 Inclusion of Sensitive Data [HIGH] [CRITICAL]

  • Description: The serializer directly includes attributes that contain sensitive information in the API response. This happens when developers fail to explicitly define which attributes should be included, relying instead on implicit inclusion or using attributes :all.
  • Example: A UserSerializer includes the password_digest attribute, exposing the hashed password to anyone making a request to the /users endpoint.
  • Why it's High-Risk:
    • Likelihood: High - Very common oversight.
    • Impact: High - Direct data breach.
    • Effort: Low - Requires only basic API requests.
    • Skill Level: Low - Basic API understanding.
    • Detection Difficulty: Medium - Requires monitoring API responses.
  • Why it's Critical: Directly leads to sensitive data exposure.
  • Mitigation:
    • Always explicitly define attributes using the attributes method in the serializer. Never rely on implicit inclusion.
    • Avoid using attributes :all.
    • Regularly review serializers to ensure they are not exposing sensitive data.

Attack Tree Path: 1.2 Attribute Exposure (via relationships) [HIGH] [CRITICAL]

  • Description: Sensitive data is exposed through a related object's serializer. Even if the primary serializer doesn't directly include sensitive attributes, a related object's serializer might, and that data gets included in the response.
  • Example: A PostSerializer includes belongs_to :author, serializer: AuthorSerializer. The AuthorSerializer includes the email and admin_notes attributes. When a Post is serialized, the author's email and admin notes are exposed.
  • Why it's High-Risk:
    • Likelihood: Medium - Common oversight, especially with complex relationships.
    • Impact: High - Data breach of related object data.
    • Effort: Low to Medium - Requires exploring related objects.
    • Skill Level: Low to Medium - Requires understanding of relationships.
    • Detection Difficulty: Medium to High - Requires analyzing multiple responses.
  • Why it's Critical: Indirectly, but effectively, leads to sensitive data exposure.
  • Mitigation:
    • Carefully manage relationships in serializers. Use include: false to exclude entire relationships.
    • Use only and except options within associations to control which attributes of related objects are included.
    • Create separate serializers for different contexts (e.g., PublicUserSerializer vs. AdminUserSerializer).
    • Review all serializers, including those used for relationships.

Attack Tree Path: 3.1 Overly Permissive Attribute Inclusion (Default or Explicit) [HIGH]

  • Description: This represents a systemic vulnerability where the application's configuration or coding practices lead to widespread inclusion of attributes, increasing the likelihood of 1.1 and 1.2. This can be due to default settings in AMS or consistent developer errors.
  • Example: A new attribute is added to a model, and developers forget to update the corresponding serializers. The new attribute is automatically included in API responses because explicit attribute definitions are not enforced.
  • Why it's High-Risk:
    • Likelihood: Medium to High - Depends on coding standards and practices.
    • Impact: High - Facilitates widespread data leakage.
    • Effort: Low - The vulnerability is inherent in the configuration.
    • Skill Level: Low - Exploitation requires no special skills.
    • Detection Difficulty: Medium - Requires auditing configurations and responses.
  • Mitigation:
    • Establish and enforce coding standards that require explicit attribute definition in all serializers.
    • Use linters and static analysis tools to detect overly permissive configurations.
    • Include serializer reviews as a mandatory part of the code review process.
    • Configure AMS to be restrictive by default, requiring explicit inclusion of attributes.