accessibility.md

Accessibility

This page analyzes the Chromium accessibility component and potential security vulnerabilities.

Component Focus:

The focus of this page is on the Chromium accessibility component, specifically how it handles accessibility information and interacts with assistive technologies. The primary file of interest is ui/views/accessibility/ax_virtual_view.cc.

Potential Logic Flaws:

• Insecure Data Handling: Vulnerabilities in how accessibility data is handled could lead to unauthorized access or data corruption.
• Man-in-the-Middle Attacks: Vulnerabilities in the communication protocol could allow an attacker to intercept and modify accessibility data.
• Incorrect Origin Handling: Incorrectly handled origins could allow a malicious website to access accessibility data from another website.
• Resource Leaks: Improper resource management could lead to memory leaks or other resource exhaustion issues.
• Bypassing Permissions: Logic flaws could allow an attacker to bypass permission checks for accessing accessibility data.
• Incorrect Data Validation: Improper validation of accessibility data could lead to vulnerabilities.
• Accessibility Spoofing: Vulnerabilities could allow a malicious actor to spoof accessibility information.

Further Analysis and Potential Issues:

The accessibility implementation in Chromium is complex, involving multiple layers of checks and balances. It is important to analyze how accessibility information is generated, managed, and used. The ax_virtual_view.cc file is a key area to investigate. This file manages virtual accessibility views in the UI framework.

• File: ui/views/accessibility/ax_virtual_view.cc
  • This file implements the AXVirtualView class, which is used to manage virtual accessibility views.
  • Key functions to analyze include: AddChildView, RemoveChildView, GetNativeObject, GetData, GetChildCount, ChildAtIndex, GetParent, GetBoundsRect, HitTestSync, GetFocus, AccessibilityPerformAction, SetPopulateDataCallback, UnsetPopulateDataCallback.
  • The AXVirtualView uses ui::AXPlatformNode to interact with the platform accessibility API.

Code Analysis:

// Example code snippet from ax_virtual_view.cc
gfx::NativeViewAccessible AXVirtualView::HitTestSync(
    int screen_physical_pixel_x,
    int screen_physical_pixel_y) const {
  if (GetData().IsInvisible())
    return nullptr;

  // Check if the point is within any of the virtual children of this view.
  // AXVirtualView's HitTestSync is a recursive function that will return the
  // deepest child, since it does not support relative bounds.
  // Search the greater indices first, since they're on top in the z-order.
  for (const std::unique_ptr<AXVirtualView>& child :
       base::Reversed(children_)) {
    gfx::NativeViewAccessible result =
        child->HitTestSync(screen_physical_pixel_x, screen_physical_pixel_y);
    if (result)
      return result;
  }

  // If it's not inside any of our virtual children, and it's inside the bounds
  // of this virtual view, then it's inside this virtual view.
  gfx::Rect bounds_in_screen_physical_pixels =
      GetBoundsRect(ui::AXCoordinateSystem::kScreenPhysicalPixels,
                    ui::AXClippingBehavior::kUnclipped);
  if (bounds_in_screen_physical_pixels.Contains(
          static_cast<float>(screen_physical_pixel_x),
          static_cast<float>(screen_physical_pixel_y)) &&
      !IsIgnored()) {
    return GetNativeObject();
  }

  return nullptr;
}

Areas Requiring Further Investigation:

• How are accessibility trees created and managed?
• How is accessibility data generated and updated?
• How are different types of accessibility events handled?
• How are errors handled during accessibility operations?
• How are resources (e.g., memory, CPU) managed?
• How is accessibility information handled in different contexts (e.g., incognito mode, extensions)?
• How is accessibility information handled across different processes?
• How is accessibility information handled for cross-origin requests?
• How does the ui::AXPlatformNode work and how does it interact with the platform accessibility API?
• How does the AXEventManager work and how are accessibility events dispatched?
• How does the ViewAccessibility class work and how is accessibility information managed for views?

Secure Contexts and Accessibility:

Secure contexts are important for accessibility. The accessibility API should only be accessible from secure contexts to prevent unauthorized access to accessibility information.

Privacy Implications:

The accessibility component has significant privacy implications. Incorrectly handled accessibility data could allow websites to access sensitive user data without proper consent. It is important to ensure that the accessibility component is implemented in a way that protects user privacy.

Additional Notes:

• The accessibility implementation is constantly evolving, so it is important to stay up-to-date with the latest changes.
• The accessibility implementation is closely tied to the security model of Chromium, so it is important to understand the overall security architecture.
• The AXVirtualView relies on ui::AXPlatformNode to interact with the platform accessibility API. The implementation of this class is important to understand.