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attack-surface.md

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Attack Surface Analysis for dart-lang/json_serializable

Attack Surface: 1. Lack of Built-in Input Sanitization leading to Injection Vulnerabilities

  • Description: json_serializable deserializes JSON data without any inherent input sanitization. If this deserialized data is directly used in sensitive operations, it can be vulnerable to injection attacks.
  • json_serializable Contribution: json_serializable's code generation focuses solely on mapping JSON to Dart objects. It does not include any mechanisms for sanitizing or validating the input data, passing raw deserialized values to the application.
  • Example: A JSON payload contains a field intended for display on a webpage: "userName": "<img src='x' onerror='alert(\"XSS\")'> ". If this userName is deserialized using json_serializable and directly rendered in HTML without escaping, it will execute the embedded JavaScript, leading to a Cross-Site Scripting (XSS) vulnerability. Similarly, unsanitized data could be used in SQL queries, leading to SQL injection.
  • Impact: Cross-Site Scripting (XSS), SQL Injection, Command Injection, and other injection-based vulnerabilities, potentially leading to data breaches, unauthorized access, or system compromise.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Output Encoding/Escaping: Always encode or escape data appropriately before using it in contexts susceptible to injection attacks. For example, use HTML escaping for web pages, parameterized queries for databases, and appropriate escaping for command-line arguments. This must be done after deserialization by json_serializable.
    • Input Validation and Sanitization: Implement explicit input validation and sanitization logic based on the context and expected data format. This might involve whitelisting allowed characters, using regular expressions to validate formats, or employing dedicated sanitization libraries. This validation should be performed on the Dart objects after they are deserialized by json_serializable.

Attack Surface: 2. Denial of Service (DoS) through Malicious JSON Payloads

  • Description: Processing extremely large, deeply nested, or complex JSON payloads can consume excessive server resources (CPU, memory), potentially leading to a Denial of Service (DoS).
  • json_serializable Contribution: json_serializable relies on dart:convert for the underlying JSON parsing. While dart:convert has some internal limitations, it can still be susceptible to resource exhaustion when parsing maliciously crafted JSON, and json_serializable does not introduce any additional safeguards against this.
  • Example: An attacker sends a JSON payload with an extremely deep level of nesting (e.g., hundreds or thousands of nested objects or arrays). When json_serializable attempts to deserialize this payload using dart:convert, it can consume excessive CPU and memory resources, potentially slowing down or crashing the application, making it unavailable to legitimate users.
  • Impact: Denial of Service, application unavailability, resource exhaustion, potentially leading to service disruption and financial losses.
  • Risk Severity: High
  • Mitigation Strategies:
    • Payload Size Limits: Implement strict limits on the maximum size of incoming JSON payloads at the application or infrastructure level (e.g., web server, API gateway).
    • Parsing Timeouts: Set timeouts for JSON parsing operations to prevent indefinite resource consumption if parsing takes an excessive amount of time.
    • Rate Limiting: Implement rate limiting on API endpoints that accept JSON data to mitigate DoS attacks from repeated malicious requests.
    • Resource Monitoring and Throttling: Monitor server resource usage (CPU, memory) and implement throttling mechanisms to limit resource consumption by individual requests or users if abnormal usage patterns are detected.

Attack Surface: 3. Polymorphism and Subtype Handling Vulnerabilities with @JsonSubtype

  • Description: When using @JsonSubtype for handling polymorphism, the application relies on a discriminator field in the JSON to determine which concrete subtype to instantiate. If this discriminator field is manipulated by an attacker, it could lead to the instantiation of unintended or potentially less secure subtypes.
  • json_serializable Contribution: @JsonSubtype is a feature provided directly by json_serializable to handle polymorphic JSON structures. The security risk arises directly from the design of @JsonSubtype which relies on an external, potentially untrusted, discriminator value in the JSON to control object instantiation.
  • Example: An application uses @JsonSubtype to handle different user roles, with subtypes like Admin and User. The JSON payload is expected to specify the role via a discriminator field. An attacker could modify the discriminator field in the JSON to force the application to instantiate a User object even when an Admin object was expected. If authorization logic relies on the instantiated object type, this could lead to an authorization bypass, granting a user unintended privileges.
  • Impact: Authorization bypass, access control vulnerabilities, instantiation of unexpected object types leading to unintended behavior, potentially granting unauthorized access to sensitive data or functionalities.
  • Risk Severity: High
  • Mitigation Strategies:
    • Strict Validation of Discriminator Field: Thoroughly validate the discriminator field in the JSON to ensure it corresponds to an expected and authorized subtype. Implement a strict whitelist of allowed discriminator values.
    • Whitelisting Allowed Subtypes: Explicitly define and whitelist the allowed subtypes for deserialization. Reject JSON payloads that attempt to instantiate subtypes not on the whitelist.
    • Principle of Least Privilege for Subtypes: Design subtypes with the principle of least privilege in mind. Ensure that even if an attacker manages to instantiate a different subtype, the impact is minimized by limiting the capabilities and permissions of each subtype.
    • Secure Discriminator Handling: Consider alternative, more secure methods for handling polymorphism if possible, that do not rely solely on a potentially untrusted discriminator value from the JSON payload. For example, using different API endpoints for different types or server-side logic to determine the correct type based on authentication and authorization context.