mitigations.md

Mitigation Strategies Analysis for jamesnk/newtonsoft.json

Mitigation Strategy: TypeNameHandling Control

Description:

1. Identify all usages: Search the codebase for all instances of JsonConvert.DeserializeObject, JsonSerializer.Deserialize, and any custom serialization logic using Newtonsoft.Json.
2. Explicitly set TypeNameHandling: In every instance where deserialization occurs, explicitly set the TypeNameHandling property within a JsonSerializerSettings object to TypeNameHandling.None.

   var settings = new JsonSerializerSettings { TypeNameHandling = TypeNameHandling.None };
   var obj = JsonConvert.DeserializeObject<MyClass>(jsonString, settings);

3. Code Review: Conduct a thorough code review to ensure that TypeNameHandling.None is consistently applied and that no code paths bypass this setting.
4. Unit Tests: Create unit tests that specifically attempt to deserialize malicious JSON payloads with type information. These tests should fail (throw an exception or return null) if TypeNameHandling.None is correctly implemented.
5. Integration Tests: Create integration tests that simulate real-world scenarios, including receiving JSON data from external sources. These tests should verify that the application correctly handles unexpected or malicious type information.

List of Threats Mitigated:

• Remote Code Execution (RCE) (Critical): Prevents attackers from injecting arbitrary code by specifying malicious types in the JSON payload.
• Object Injection (High): Prevents the creation of unauthorized objects, even if they don't directly lead to RCE.

Impact:

• RCE: Risk reduced from Critical to Negligible (assuming no other vulnerabilities exist). This is the most important mitigation.
• Object Injection: Risk reduced from High to Low.

Currently Implemented:

• Describe where this is already implemented (e.g., "Implemented in UserController.ProcessData method, OrderService.DeserializeOrder method"). Provide specific file paths and method names.
• Example: "Implemented in all API endpoints handling user input (Controllers/UserController.cs, Controllers/ProductController.cs)."

Missing Implementation:

• Describe where this is not yet implemented (e.g., "Missing in legacy ReportGenerator class, which still uses default settings"). Provide specific file paths and method names.
• Example: "Missing in the internal reporting module (Services/ReportingService.cs, specifically the GenerateReportFromJson method)."

Mitigation Strategy: MaxDepth Restriction

Description:

1. Analyze Data Structures: Determine the maximum expected nesting depth for legitimate JSON data in your application.
2. Set MaxDepth: In JsonSerializerSettings, set the MaxDepth property to a value slightly above the expected maximum. Start with a conservative value (e.g., 32) and adjust as needed.

   var settings = new JsonSerializerSettings { MaxDepth = 32 };
   var obj = JsonConvert.DeserializeObject<MyClass>(jsonString, settings);

3. Error Handling: Implement robust error handling to gracefully handle cases where the MaxDepth limit is exceeded. Log the error and return an appropriate error response to the user (don't expose internal error details).
4. Unit Tests: Create unit tests that send JSON payloads with varying nesting depths, including depths exceeding the configured MaxDepth. Verify that the application correctly rejects overly deep JSON.

List of Threats Mitigated:

• Denial of Service (DoS) via Stack Overflow (Medium): Prevents attackers from crashing the application by sending deeply nested JSON.

Impact:

• DoS: Risk reduced from Medium to Low.

Currently Implemented:

• Example: "Implemented globally in a middleware component that preprocesses all incoming requests (Middleware/JsonInputMiddleware.cs)."

Missing Implementation:

• Example: "Missing in direct calls to JsonConvert.DeserializeObject within unit tests (Tests/MyServiceTests.cs)."

Mitigation Strategy: Input Size Limits (MaxStringContentLength, MaxArrayLength)

Description:

1. Determine Reasonable Limits: Analyze your application's data requirements to determine reasonable maximum lengths for strings and arrays within JSON payloads.
2. Set Limits: In JsonSerializerSettings, set MaxStringContentLength and MaxArrayLength to appropriate values.

   var settings = new JsonSerializerSettings {
       MaxStringContentLength = 1024 * 1024, // 1MB
       MaxArrayLength = 10000
   };
   var obj = JsonConvert.DeserializeObject<MyClass>(jsonString, settings);

3. Error Handling: Implement error handling to gracefully handle cases where these limits are exceeded.
4. Unit Tests: Create unit tests that send JSON payloads with strings and arrays of varying sizes, including sizes exceeding the configured limits.

List of Threats Mitigated:

• Denial of Service (DoS) via Memory Exhaustion (Medium): Prevents attackers from consuming excessive memory by sending large strings or arrays.

Impact:

• DoS: Risk reduced from Medium to Low.

Currently Implemented:

• Example: "Implemented in the JsonSerializationHelper class, which is used by all services that deserialize JSON (Helpers/JsonSerializationHelper.cs)."

Missing Implementation:

• Example: "Missing in a legacy component that directly reads JSON from a file (Legacy/FileProcessor.cs)."

Mitigation Strategy: Date and Time Handling

Description:

1. Choose Consistent Handling: Decide on a consistent approach for handling dates and times. Using DateTimeOffset and DateTimeZoneHandling.Utc is generally recommended for security and consistency.
2. Explicitly Configure: In JsonSerializerSettings, set DateParseHandling and DateTimeZoneHandling to your chosen values.

   var settings = new JsonSerializerSettings {
       DateParseHandling = DateParseHandling.DateTimeOffset,
       DateTimeZoneHandling = DateTimeZoneHandling.Utc
   };

3. Avoid Ambiguity: Avoid using ambiguous date formats in your JSON data. Use ISO 8601 format (e.g., "2023-10-27T10:00:00Z").
4. Unit Tests: Create unit tests that cover various date and time formats, time zones, and edge cases (e.g., leap years, daylight saving time transitions).

List of Threats Mitigated:

• Data Corruption/Inconsistency (Low to Medium): Prevents issues arising from incorrect date/time parsing or time zone conversions. Severity depends on the application's reliance on accurate date/time data.
• Potential Logic Errors (Low): Reduces the risk of unexpected behavior due to inconsistent date/time handling.

Impact:

• Data Corruption/Inconsistency: Risk reduced from Low/Medium to Negligible.
• Potential Logic Errors: Risk reduced from Low to Negligible.

Currently Implemented:

• Example: "Implemented in the base class for all API models (Models/BaseModel.cs), ensuring consistent date/time handling across the application."

Missing Implementation:

• Example: "Missing in a utility class that parses dates from a third-party API response (Utilities/ThirdPartyApiHelper.cs)."

Mitigation Strategy: Serialization Binder (If TypeNameHandling is unavoidable)

Description:

1. Identify Absolutely Necessary Uses: Rigorously review all code using TypeNameHandling. Justify each instance. If possible, refactor to eliminate the need for TypeNameHandling.
2. Implement a Custom ISerializationBinder: Create a class that implements the ISerializationBinder interface. This class will control which types are allowed to be deserialized.

   // (See example in previous response)

3. Whitelist Approach: In the BindToType method, only return a Type object for explicitly allowed types. Return null (or throw an exception) for all other types. Never trust type information from the input JSON.
4. Configuration: Set the SerializationBinder property of your JsonSerializerSettings to an instance of your custom binder.

   var settings = new JsonSerializerSettings {
       TypeNameHandling = TypeNameHandling.Auto, // Or Objects, Arrays, etc. as needed.
       SerializationBinder = new MyCustomBinder()
   };

5. Unit/Integration Tests: Create tests that attempt to deserialize various types, including both allowed and disallowed types. Verify that only allowed types are successfully deserialized.

List of Threats Mitigated:

• Remote Code Execution (RCE) (Critical): Reduces the risk, but does not eliminate it. A flawed binder can still be exploited.
• Object Injection (High): Reduces the risk by limiting the types that can be created.

Impact:

• RCE: Risk reduced from Critical to High (or Medium, depending on the binder's robustness). This is not a foolproof solution.
• Object Injection: Risk reduced from High to Medium.

Currently Implemented:

• Example: "A custom SerializationBinder is used in the LegacyIntegrationService to handle polymorphic data from an external system (Services/LegacyIntegrationService.cs)."

Missing Implementation:

• Example: "No SerializationBinder is used in other parts of the application that might require TypeNameHandling (identified during code review)."