payment_handler.md

Payment Handler

This page analyzes the Chromium Payment Handler component and potential security vulnerabilities.

Component Focus:

The focus of this page is on the Chromium Payment Handler component, specifically how it handles payment requests and interacts with payment apps. The primary file of interest is chrome/browser/ui/views/payments/payment_handler_web_flow_view_controller.cc.

Potential Logic Flaws:

• Insecure Payment Data Handling: Vulnerabilities in how payment 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 payment requests.
• Incorrect Origin Handling: Incorrectly handled origins could allow a malicious website to initiate payment requests on behalf of 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 payment apps.
• Incorrect Data Validation: Improper validation of payment data could lead to vulnerabilities.
• UI Spoofing: Vulnerabilities could allow a malicious actor to spoof the payment handler UI.

Further Analysis and Potential Issues:

The Payment Handler implementation in Chromium is complex, involving multiple layers of checks and balances. It is important to analyze how payment requests are processed, how payment apps are invoked, and how data is transferred. The payment_handler_web_flow_view_controller.cc file is a key area to investigate. This file manages the UI for payment handlers in a web flow.

• File: chrome/browser/ui/views/payments/payment_handler_web_flow_view_controller.cc
  • This file manages the UI for payment handlers in a web flow.
  • Key functions to analyze include: FillContentView, PopulateSheetHeaderView, VisibleSecurityStateChanged, AddNewContents, HandleKeyboardEvent, DidFinishNavigation, LoadProgressChanged, TitleWasSet, AbortPayment.
  • The PaymentHandlerWebFlowViewController uses PaymentRequestSheetController to manage the payment sheet.
  • The RoundedCornerViewClipper class is used to clip the corners of the WebView.

Code Analysis:

// Example code snippet from payment_handler_web_flow_view_controller.cc
void PaymentHandlerWebFlowViewController::FillContentView(
    views::View* content_view) {
  // The first time this is called, also create and add the header/content
  // separator container children.  This must be done before calling
  // LoadInitialURL() below so these will be set up before that calls back to
  // LoadProgressChanged(), and it can't be done in the constructor since the
  // container doesn't exist yet.
  if (!progress_bar_) {
    // Add the progress bar to the separator container. The progress bar
    // colors will be set in PopulateSheetHeaderView.
    progress_bar_ = header_content_separator_container()->AddChildView(
        std::make_unique<views::ProgressBar>());
    progress_bar_->SetPreferredHeight(2);
  }

  content_view->SetLayoutManager(std::make_unique<views::FillLayout>());

  auto* web_view =
      content_view->AddChildView(std::make_unique<views::WebView>(profile_));
  rounded_corner_clipper_ =
      std::make_unique<RoundedCornerViewClipper>(web_view, dialog());

  // Set up the WebContents that is inside the views::WebView, which hosts the
  // payment app.
  Observe(web_view->GetWebContents());
  PaymentHandlerNavigationThrottle::MarkPaymentHandlerWebContents(
      web_contents());
  web_contents()->SetDelegate(this);
  DCHECK_NE(log_.web_contents(), web_contents());
  content::PaymentAppProvider::GetOrCreateForWebContents(
      /*payment_request_web_contents=*/log_.web_contents())
      ->SetOpenedWindow(
          /*payment_handler_web_contents=*/web_contents());

  web_view->LoadInitialURL(target_);
  // ... more logic ...
}

Areas Requiring Further Investigation:

• How are payment apps discovered and selected?
• How is payment data validated and sanitized?
• How is the communication between the browser process and the payment app secured?
• How are origins validated?
• How are errors handled during the payment process?
• How are resources (e.g., memory, network) managed?
• How are payment handlers handled in different contexts (e.g., incognito mode, extensions)?
• How are payment handlers handled across different processes?
• How are payment handlers handled for cross-origin requests?
• How does the PaymentRequestSheetController work and how is the payment sheet managed?
• How does the SslValidityChecker work and how is the security of the page verified?

Secure Contexts and Payment Handler:

Secure contexts are important for the Payment Handler API. The Payment Handler API should only be accessible from secure contexts to prevent unauthorized access to payment data.

Privacy Implications:

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

Additional Notes:

• The Payment Handler implementation is constantly evolving, so it is important to stay up-to-date with the latest changes.
• The Payment Handler implementation is closely tied to the security model of Chromium, so it is important to understand the overall security architecture.
• The PaymentHandlerWebFlowViewController relies on several other components, such as PaymentRequestSheetController and SslValidityChecker, to perform its tasks. The implementation of these components is also important to understand.