threat-modeling.md

Threat Model Analysis for doctrine/instantiator

Threat: Threat 1: Bypassing Constructor Security Checks

• Description: An attacker crafts input that causes the application to instantiate a class using Instantiator::instantiate() without calling its constructor. The constructor of this class is intended to perform crucial security checks. These checks might include:

  • Validating input parameters that are normally passed to the constructor.
  • Initializing security-related properties to safe default values (e.g., setting an isAdmin flag to false, initializing a cryptographic key).
  • Enforcing access control rules that are normally checked within the constructor.
  • Setting up required dependencies or resources in a secure manner.

  By bypassing the constructor, the attacker avoids these intended security measures, leaving the object in an insecure or unpredictable state. The attacker does not necessarily need to control the class name directly; they might exploit existing application logic that uses Instantiator on a class that should have constructor checks.

• Impact:

  • Privilege Escalation: If the constructor sets default security roles or permissions (e.g., isAdmin = false), bypassing it could leave the object in an unintentionally privileged state. The property might be null, false (in some loose comparison contexts), or even retain a value from a previous object in memory.
  • Data Corruption/Injection: If the constructor validates input parameters to prevent injection vulnerabilities, bypassing it could allow an attacker to inject malicious data directly into object properties.
  • Information Disclosure: If the constructor is responsible for securely initializing sensitive data (e.g., an encryption key), bypassing it could leave that data uninitialized, predictable, or accessible to the attacker.
  • Violation of Business Logic and Invariants: The constructor often enforces critical business rules and ensures the object is in a consistent state. Bypassing it can lead to an inconsistent or invalid application state, potentially causing unexpected behavior or crashes.

• Affected Instantiator Component: Instantiator::instantiate() (the core function of the library that bypasses the constructor).

• Risk Severity: Critical

• Mitigation Strategies:

  • Defensive Property Initialization: Use type hints and default values for properties whenever possible. This ensures properties have a safe default state even if the constructor is bypassed. Example: private bool $isAdmin = false; This is a primary mitigation.
  • Lazy Initialization (for Critical Properties): If a property must be initialized in a specific, secure way (e.g., with a cryptographically secure random value), use lazy initialization within getter methods. This ensures the property is initialized only when it's actually accessed, regardless of whether the constructor was called. This is crucial for sensitive data.
  • Post-Instantiation Validation (Defense-in-Depth): After using Instantiator::instantiate(), use reflection (PHP's ReflectionClass and ReflectionProperty) to inspect the object's state and verify that critical properties have been initialized to expected, safe values. This is a secondary mitigation, adding an extra layer of security. It adds overhead, so use it judiciously.
  • Strict Input Validation (Class Name Whitelisting): If the class name to be instantiated comes from any form of user input (direct or indirect), strictly validate it against a pre-approved whitelist of allowed classes. Never allow arbitrary class instantiation based on user-supplied data. This is crucial if user input influences the instantiation process.
  • Avoid Constructor-Only Security: Do not rely exclusively on the constructor for security-critical operations. Design your classes to be secure even if the constructor is bypassed. This is a fundamental principle of secure design.
  • Factory Methods with Validation: If Instantiator is needed, encapsulate its use within factory methods. These factory methods can perform pre-instantiation validation of the class name and any necessary post-instantiation checks, ensuring a secure object creation process.

Threat: Threat 2: Exploiting Uninitialized State in Deserialization Contexts (Indirect, but Instantiator-Facilitated)

• Description: While the primary vulnerability here is unsafe deserialization, Instantiator exacerbates the risk. An attacker provides malicious serialized data. The application uses unserialize(). If the application then uses Instantiator::instantiate() on the deserialized object (or a class specified within the serialized data), it bypasses the constructor, compounding the problem. The attacker gains control over the object's state and avoids constructor-based security checks. This is a high risk because it combines two dangerous practices. The attacker is leveraging Instantiator to make an already bad situation (unsafe deserialization) much worse.
• Impact:
  • Remote Code Execution (RCE): If combined with a class that has exploitable "magic methods" (__wakeup, __destruct, etc.), this can lead to RCE, even without the constructor being called.
  • Arbitrary Object Manipulation: The attacker can create objects with arbitrary property values, leading to data corruption, logic errors, and potential privilege escalation.
  • All Impacts of Threat 1: All the impacts of bypassing constructor security checks (Threat 1) are also present and amplified in this scenario.
• Affected Instantiator Component: Instantiator::instantiate() (when used in conjunction with, or after, unserialize()).
• Risk Severity: High
• Mitigation Strategies:
  • Avoid Unsafe Deserialization: The primary mitigation is to never deserialize data from untrusted sources. This is the most critical step.
  • Use Safe Alternatives to Deserialization: Use safer data exchange formats like JSON (with json_decode() and strict schema validation) or Protocol Buffers. These are significantly less prone to injection vulnerabilities.
  • Strict Class Name Whitelisting (If Deserialization is Unavoidable): If you absolutely must use unserialize(), implement a very strict whitelist of allowed classes that can be deserialized. This whitelist should be as restrictive as possible.
  • Avoid Magic Methods with Side Effects: Be extremely cautious about using magic methods (especially __wakeup and __destruct) in classes that might be deserialized. These methods are frequent targets for exploitation. If you must use them, thoroughly sanitize any data used within these methods.
  • Combine with Mitigations from Threat 1: All the mitigation strategies for Threat 1 (defensive property initialization, lazy initialization, post-instantiation validation) are also crucial in this scenario to minimize the impact of bypassing the constructor.
  • Input Validation Before Deserialization: Perform basic validation on the serialized data before passing it to unserialize(). Check for length, structure, or known malicious patterns. This is a defense-in-depth measure.