Skip to content

Latest commit

 

History

History
135 lines (110 loc) · 14.1 KB

mitigations.md

File metadata and controls

135 lines (110 loc) · 14.1 KB

Mitigation Strategies Analysis for avaloniaui/avalonia

Mitigation Strategy: Rigorous Input Validation and Sanitization for Custom Controls

  • Description:

    1. Identify Custom Controls: List all custom controls within the Avalonia application that directly handle user input (e.g., custom text boxes, drawing surfaces, specialized input fields that subclass Avalonia controls or implement custom rendering).
    2. Define Expected Input: For each custom control, clearly define the expected data type, format, range, and any other constraints for the input. Document these expectations specifically in relation to how Avalonia handles the input.
    3. Implement Validation Logic: Within the custom control's Avalonia-specific event handlers (e.g., TextInput, KeyDown, PointerPressed, PointerMoved, PointerReleased), implement validation logic before the input is used in any operation or stored in an Avalonia property. This logic should:
      • Type Checking: Verify that the input is of the correct data type expected by the Avalonia property.
      • Range Checking: Ensure numerical values fall within Avalonia property limits.
      • Format Validation: Use regular expressions to enforce formats, considering how Avalonia will interpret the input (e.g., for Brush properties).
      • Length Restrictions: Limit string lengths, considering Avalonia's rendering limitations.
      • Character Whitelisting/Blacklisting: Allow/disallow characters, focusing on characters that have special meaning within Avalonia's XAML or styling system.
      • Sanitization: Remove or escape characters that could interfere with Avalonia's parsing or rendering (e.g., escaping characters that could be interpreted as XAML markup).
    4. Error Handling: Provide clear error messages within the Avalonia UI (e.g., using tooltips, validation error styles). Do not expose internal error details. Log validation failures.
    5. Test Thoroughly: Create Avalonia-specific UI tests (using a framework like Avalonia.Headless or by interacting with the running application) that specifically target the input validation logic of each custom control, covering valid and invalid input, and verifying the UI's response.

  • Threats Mitigated:

    • Avalonia-Specific XAML Injection (High Severity): Prevents malicious XAML code from being injected through custom controls and interpreted by Avalonia's XAML parser. This is distinct from general XSS, as it targets Avalonia's rendering engine.
    • Avalonia Property Manipulation (High Severity): Prevents attackers from setting Avalonia properties to unexpected or invalid values that could cause crashes, unexpected behavior, or security vulnerabilities within Avalonia's rendering or layout system.
    • Denial of Service (DoS) against Avalonia (Medium Severity): Prevents attackers from causing Avalonia's rendering or layout engine to crash or become unresponsive by providing excessively large, complex, or malformed inputs to custom controls.
    • Data Corruption within Avalonia's State (Medium Severity): Prevents invalid data from being stored in Avalonia's internal data structures, which could lead to rendering errors or unexpected behavior.

  • Impact:

    • Avalonia-Specific XAML Injection: Risk significantly reduced (near elimination if implemented correctly).
    • Avalonia Property Manipulation: Risk significantly reduced (near elimination if implemented correctly).
    • DoS against Avalonia: Risk reduced (effectiveness depends on the specific validation checks).
    • Data Corruption within Avalonia's State: Risk reduced.

  • Currently Implemented:

    • CustomNumericInputControl (subclasses TextBox) has basic range checking, but doesn't consider Avalonia-specific limits.
    • CustomDrawingControl (implements custom drawing) has no input validation.
    • CustomFilenameInput (subclasses TextBox) has basic length restriction, but no Avalonia-specific sanitization.

  • Missing Implementation:

    • CustomDrawingControl needs complete input validation, specifically considering how Avalonia handles drawing commands and coordinates.
    • CustomFilenameInput needs Avalonia-specific sanitization to prevent characters that could interfere with Avalonia's resource loading.
    • All custom controls need Avalonia-specific UI tests.

Mitigation Strategy: Secure Data Binding with ViewModels (Avalonia-Specific Considerations)

  • Description:

    1. Identify Risky Bindings: Review all Avalonia data bindings, focusing on those that bind data from any source to Avalonia properties that could affect rendering, layout, styling, or control behavior. Pay special attention to bindings to Style, Template, Content, and properties that accept complex Avalonia types (e.g., Brush, Geometry).
    2. Implement ViewModels: Use ViewModels for all views, ensuring that all data bound to Avalonia properties flows through the ViewModel.
    3. Avalonia-Specific Data Validation in ViewModel: In the ViewModel, validate and sanitize properties specifically for how Avalonia will interpret them. This includes:
      • Type Compatibility: Ensure data types are compatible with the target Avalonia property.
      • Avalonia Value Constraints: Validate against any constraints imposed by Avalonia on the property (e.g., valid Brush values, valid Geometry syntax).
      • XAML Injection Prevention: Sanitize string data to prevent injection of malicious XAML markup, especially for properties like Content or Style.
      • Resource Key Validation: If binding to resource keys, ensure the keys are valid and point to trusted resources.
    4. Bind to ViewModel Properties: In the XAML, bind Avalonia UI elements only to the validated and sanitized properties of the ViewModel.
    5. Avoid Direct Binding to Sensitive Avalonia Properties: Never bind directly from untrusted sources to Avalonia properties that control styling, templates, content (if the content is not plain text), or resource loading.
    6. Test ViewModel Validation (Avalonia Context): Create unit tests that verify the ViewModel's validation logic, considering how Avalonia will interpret the validated data.

  • Threats Mitigated:

    • Avalonia-Specific XAML Injection (High Severity): Prevents XAML injection through data binding, targeting Avalonia's rendering engine.
    • Avalonia Style/Template Manipulation (High Severity): Prevents attackers from modifying the application's appearance or behavior by injecting malicious styles or templates through data binding.
    • Avalonia Resource Hijacking (High Severity): Prevents attackers from replacing legitimate resources with malicious ones by manipulating resource keys through data binding.
    • Denial of Service (DoS) against Avalonia (Medium Severity): Prevents DoS attacks that exploit vulnerabilities in Avalonia's handling of styles, templates, or resources.

  • Impact:

    • Avalonia-Specific XAML Injection: Risk significantly reduced.
    • Avalonia Style/Template Manipulation: Risk significantly reduced.
    • Avalonia Resource Hijacking: Risk significantly reduced.
    • DoS against Avalonia: Risk reduced.

  • Currently Implemented:

    • MainWindowViewModel has some validation, but not specifically focused on Avalonia's interpretation of the data.
    • SettingsViewModel has no Avalonia-specific validation.

  • Missing Implementation:

    • SettingsViewModel needs validation for all settings, considering how Avalonia uses them (e.g., for styling or resource loading).
    • All ViewModels need Avalonia-aware unit tests.
    • Review all data bindings to ensure they are using ViewModels and not binding directly to sensitive Avalonia properties.

Mitigation Strategy: Restrict Dynamic XAML Loading (Avalonia-Specific)

  • Description:

    1. Identify Dynamic XAML Loading: Find all instances where Avalonia XAML is loaded dynamically (using AvaloniaXamlLoader.Load or similar).
    2. Eliminate Untrusted Sources: If possible, eliminate dynamic XAML loading from untrusted sources. Load Avalonia XAML only from embedded resources within the application assembly.
    3. Avalonia-Specific Sandboxing (If Necessary): If dynamic XAML loading is unavoidable, use a restricted AvaloniaXamlLoader configuration:
      • Whitelist Allowed Avalonia Types: Create a whitelist of allowed Avalonia control types, property types, and markup extensions that can be loaded.
      • Disable Dangerous Avalonia Features: Disable features that could be exploited, such as binding to arbitrary methods, creating instances of arbitrary types, or using certain markup extensions. Specifically restrict access to Avalonia's styling and templating system.
      • Isolate in a Separate Context: Consider using a separate TopLevel or window for dynamically loaded content, limiting its interaction with the main application.
    4. Sanitize Input (Extremely Difficult - Avoid): If XAML is constructed from user input, thorough sanitization is required, but this is extremely difficult to do reliably and securely for Avalonia XAML. Avoid this if at all possible.
    5. Test Loading Restrictions (Avalonia UI Tests): Create Avalonia UI tests that verify the restrictions on dynamic XAML loading are working as expected, attempting to load malicious XAML and confirming that it is rejected.

  • Threats Mitigated:

    • Avalonia-Specific Code Injection (High Severity): Prevents attackers from injecting arbitrary code by loading malicious Avalonia XAML that exploits vulnerabilities in Avalonia's XAML parser or control implementations.
    • Avalonia XAML Injection (High Severity): Prevents injection of malicious XAML that could alter the application's UI, behavior, or styling in unintended ways.
    • Denial of Service (DoS) against Avalonia (Medium Severity): Prevents DoS attacks that exploit vulnerabilities in Avalonia's XAML parsing or rendering.

  • Impact:

    • Avalonia-Specific Code Injection: Risk significantly reduced (near elimination if loading only from trusted sources).
    • Avalonia XAML Injection: Risk significantly reduced (near elimination if loading only from trusted sources).
    • DoS against Avalonia: Risk reduced.

  • Currently Implemented:

    • No dynamic XAML loading is currently used.

  • Missing Implementation:

    • If dynamic XAML loading is introduced, implement the Avalonia-specific sandboxing and sanitization measures.

Mitigation Strategy: Secure Custom Drawing and Rendering (Avalonia-Specific)

  • Description: 1. Identify Custom Drawing: Locate all instances where custom drawing is performed using Avalonia's DrawingContext (e.g., within a custom control's Render override). 2. Validate Drawing Parameters: Before using any user-provided data to control drawing operations (e.g., coordinates, sizes, colors, paths), rigorously validate the data:

    • Type and Range Checks: Ensure numerical values are within acceptable ranges for Avalonia's rendering engine.
    • Geometry Validation: If drawing paths or geometries, validate the geometry data to prevent excessively complex or malformed geometries that could cause performance issues or crashes. Use Avalonia's geometry validation APIs if available.
    • Color Validation: If accepting color input, validate the color values to prevent unexpected or invalid colors.
    • Resource Validation: If using brushes or pens from external sources, validate that they are loaded from trusted sources and are of expected types. 3. Limit Drawing Complexity: Implement limits on the complexity of drawing operations based on user input. For example:
    • Maximum Path Length: Limit the number of points or segments in a path.
    • Maximum Shape Size: Limit the dimensions of shapes.
    • Maximum Number of Drawing Operations: Limit the total number of drawing calls within a single Render call. 4. Resource Management: Carefully manage resources used during drawing (e.g., brushes, pens, geometries). Dispose of resources when they are no longer needed to prevent memory leaks. 5. Test Rendering Logic (Avalonia UI Tests): Create Avalonia UI tests that specifically target the custom drawing logic, covering both valid and invalid input scenarios, and verifying that the rendering is correct and does not cause crashes or performance issues. Use visual comparisons to ensure rendering is as expected.

  • Threats Mitigated:

    • Denial of Service (DoS) against Avalonia (Medium Severity): Prevents attackers from causing Avalonia's rendering engine to crash or become unresponsive by providing excessively complex or malformed drawing instructions.
    • Avalonia Rendering Errors (Medium Severity): Prevents unexpected rendering artifacts or errors caused by invalid drawing parameters.
    • Resource Exhaustion (Medium Severity): Prevents memory leaks or excessive resource consumption caused by uncontrolled drawing operations.

  • Impact:

    • DoS against Avalonia: Risk significantly reduced.
    • Avalonia Rendering Errors: Risk significantly reduced.
    • Resource Exhaustion: Risk reduced.

  • Currently Implemented:

    • CustomDrawingControl has no input validation or complexity limits.

  • Missing Implementation:

    • CustomDrawingControl needs complete input validation and complexity limits, specifically tailored to Avalonia's DrawingContext and rendering capabilities.
    • Avalonia UI tests are needed to verify the rendering logic and resource management.