mitigations.md

Mitigation Strategies Analysis for isaacs/inherits

Mitigation Strategy: Object.freeze() and Object.seal() on Inherited Prototypes

Description:

1. Identify Target Prototypes: Immediately after using inherits(SubClass, BaseClass) to establish the inheritance relationship, identify the prototypes you need to protect. This always includes SubClass.prototype and usually BaseClass.prototype.
2. Apply Object.freeze(): Call Object.freeze(SubClass.prototype) and Object.freeze(BaseClass.prototype). This makes these prototypes non-writable, non-configurable, and non-extensible. This prevents any subsequent modification, including adding new properties or changing existing ones.
3. Consider Object.seal() (Less Secure): If you absolutely must allow modification of existing property values on the prototype (but not adding or deleting properties), use Object.seal() instead of Object.freeze(). This is less secure, so Object.freeze() is strongly preferred.
4. Critical Timing: The timing is crucial. Apply Object.freeze() or Object.seal() immediately after the inherits call and before any untrusted code or data can interact with instances of SubClass or BaseClass.

Threats Mitigated:

• Prototype Pollution: (Severity: Critical) - This directly prevents prototype pollution on the prototypes that are frozen or sealed. Since inherits sets up the prototype chain, this mitigation is directly tied to its use. If an attacker tries to modify a frozen prototype, a TypeError will be thrown (in strict mode).

Impact:

• Prototype Pollution: Risk is eliminated for the frozen/sealed prototypes. This is the most effective mitigation for prototype pollution specifically related to the inheritance chain established by inherits.

Currently Implemented:

• Implemented for the BaseEntity class and its direct subclasses (User, Product). The prototypes are frozen immediately after the inherits call.

Missing Implementation:

• Missing for the Comment class, which inherits from BaseEntity indirectly. The intermediate class and Comment.prototype are not frozen.

Mitigation Strategy: Prevent Circular Inheritance (When Using inherits Dynamically)

Description:

• Avoid Dynamic inherits: The best mitigation is to avoid using inherits dynamically based on untrusted input. If the inheritance structure is known at development time, define it statically.
• Depth-Limited inherits (If Dynamic is Unavoidable): If you must use inherits dynamically (which is a high-risk pattern), implement a strict depth limit. This means tracking how many times inherits has been called in a chain and throwing an error if a predefined limit is exceeded. This prevents an attacker from causing a stack overflow by providing input that creates a deeply nested or circular inheritance chain.
  1. Maintain a counter (e.g., in a closure or a dedicated module) to track the inheritance depth.
  2. Increment the counter before each call to inherits.
  3. Check if the counter exceeds a predefined maximum depth (e.g., 10).
  4. If the limit is exceeded, throw an error before calling inherits.
  5. Decrement the counter after the inherits call (in a finally block to ensure it's always decremented).

Threats Mitigated:

• Denial of Service (DoS) via Circular Inheritance: (Severity: Medium) - Prevents a specific type of DoS attack where an attacker could cause a stack overflow by crafting input that leads to a circular inheritance chain when inherits is used dynamically.

Impact:

• DoS: Risk is significantly reduced or eliminated, depending on the implementation of the depth limit.

Currently Implemented:

• The application's inheritance structure is defined statically; inherits is not used dynamically based on any external input.

Missing Implementation:

• No specific missing implementation, as the current design avoids dynamic use of inherits. If dynamic usage were introduced, the depth-limiting strategy would be essential.