attack-surface.md

Attack Surface Analysis for marcuswestin/webviewjavascriptbridge

Attack Surface: Insecure Message Handling

• Description: Vulnerabilities arising from insecure communication between Javascript in the WebView and native code via the bridge. This includes risks related to message interception, manipulation, and injection.
• webviewjavascriptbridge Contribution: webviewjavascriptbridge establishes the communication channel. If the implementation lacks security measures, the bridge becomes the pathway for insecure message exchange, directly contributing to this attack surface.
• Example: An attacker intercepts communication between the WebView and native app. Observing plain text messages transmitted via webviewjavascriptbridge, they inject a crafted message to trigger a native handler that grants unauthorized access to user location data.
• Impact:
  • Data Breach: Interception and decryption of sensitive data transmitted through the bridge, leading to unauthorized disclosure.
  • Unauthorized Actions: Manipulation or injection of messages causing unintended native function calls and actions.
  • Compromise of Native Resources: Malicious messages exploiting insecure handling to gain access to protected native resources.
• Risk Severity: High
• Mitigation Strategies:
  • Encrypt Bridge Communication: Implement encryption for all messages exchanged through the webviewjavascriptbridge. This should be a priority if sensitive data is handled.
  • Message Integrity Checks: Utilize message authentication codes (MACs) or digital signatures to ensure message integrity and detect tampering during transit via the bridge.
  • Minimize Sensitive Data Transmission: Reduce the amount of sensitive data transmitted through the bridge. Explore alternative, more secure methods for handling sensitive information if possible.

Attack Surface: Unrestricted Handler Registration

• Description: Allowing arbitrary Javascript code to register native handlers without proper authorization or validation, leading to potential exposure of native functionalities.
• webviewjavascriptbridge Contribution: webviewjavascriptbridge provides the API for Javascript to register handlers. If the application doesn't implement strict controls on this registration process, the bridge directly enables this vulnerability.
• Example: Malicious Javascript within the WebView uses webviewjavascriptbridge to register a handler named "executeShellCommand". If the native side blindly registers this handler without validation, the malicious Javascript can then invoke it to execute arbitrary shell commands on the device.
• Impact:
  • Arbitrary Code Execution (Native): Malicious Javascript registering handlers that result in arbitrary code execution within the native application context.
  • Privilege Escalation: Gaining elevated privileges by exploiting registered handlers to access native functionalities beyond intended web application permissions.
  • Device Compromise: Potential for full device compromise if handlers allow execution of system-level commands or access to critical resources.
• Risk Severity: Critical
• Mitigation Strategies:
  • Whitelist Allowed Handlers: Implement a strict whitelist of permitted handler names that Javascript can register via webviewjavascriptbridge.
  • Centralized Native-Side Registration: Control handler registration exclusively from the native side. Limit or eliminate Javascript's ability to directly register handlers through the bridge.
  • Authentication/Authorization for Registration: Require authentication or authorization on the native side before allowing any handler registration requests originating from Javascript via the bridge.
  • Rigorous Code Review: Thoroughly review native code handling handler registration to ensure proper validation and prevent unauthorized registration.

Attack Surface: Handler Input Validation Vulnerabilities

• Description: Native handlers failing to properly validate and sanitize input received from Javascript via webviewjavascriptbridge, leading to injection attacks and other input-based exploits.
• webviewjavascriptbridge Contribution: webviewjavascriptbridge is the conduit for data transfer from Javascript to native handlers. If handlers trust this input implicitly, the bridge becomes the vector for exploiting input validation flaws.
• Example: A native handler designed to process user-provided URLs receives input from Javascript via webviewjavascriptbridge. Without validation, malicious Javascript sends a URL containing command injection payloads. The handler, processing this unsanitized input, executes the injected commands on the native system.
• Impact:
  • Command Injection: Execution of arbitrary system commands due to unsanitized input passed through the bridge to native handlers.
  • Path Traversal: Accessing unauthorized files or directories on the device by manipulating file paths passed through the bridge.
  • SQL Injection (if applicable): Manipulation of database queries if handlers interact with databases and use unsanitized input from the bridge.
  • Buffer Overflow (Native): Potential for buffer overflows in native code if handlers don't properly handle input size from the bridge.
• Risk Severity: High
• Mitigation Strategies:
  • Mandatory Input Validation and Sanitization: Implement strict input validation and sanitization within every native handler receiving data from Javascript via webviewjavascriptbridge.
  • Principle of Least Privilege (Handler Design): Design handlers to operate with the minimum necessary privileges. Limit the scope of actions handlers can perform, even if input validation fails.
  • Secure Coding Practices (Native Handlers): Adhere to secure coding practices in native handler implementations, including using parameterized queries for databases, safe APIs for system calls, and robust error handling.
  • Regular Security Testing: Conduct regular security testing and penetration testing specifically targeting native handlers and their input handling from the bridge.

Attack Surface: Javascript Injection Leveraging the Bridge (XSS to Native Code Execution)

• Description: Exploiting Cross-Site Scripting (XSS) vulnerabilities in the web application loaded in the WebView to inject malicious Javascript that then utilizes webviewjavascriptbridge to achieve native code execution.
• webviewjavascriptbridge Contribution: webviewjavascriptbridge dramatically amplifies the impact of XSS vulnerabilities. Without the bridge, XSS is typically limited to the web context. With the bridge, XSS can escalate to native code execution, making it a critical attack vector.
• Example: A web application within the WebView has an XSS flaw. An attacker injects malicious Javascript. This Javascript uses webviewjavascriptbridge to call a legitimate-looking native handler, but crafts the call in a way that exploits a vulnerability (e.g., input validation issue) in that handler, leading to native code execution and device takeover.
• Impact:
  • Escalated XSS Impact: XSS vulnerabilities becoming a pathway to native code execution and full device compromise due to the bridge's capabilities.
  • Circumvention of Web Security: Bypassing typical web application security boundaries to directly attack the native application and device through the bridge.
  • Native Data Exfiltration: Malicious Javascript using the bridge to access and exfiltrate sensitive data stored natively on the device.
• Risk Severity: Critical
• Mitigation Strategies:
  • Aggressive XSS Prevention: Implement robust and comprehensive XSS prevention measures in the web application loaded in the WebView. Prioritize secure coding practices, input sanitization, output encoding, and Content Security Policy (CSP).
  • Defense in Depth (Handler Security): Even with XSS prevention, assume XSS might occur. Design native handlers to be resilient to malicious input and limit their capabilities to minimize the impact of potential XSS exploitation via the bridge.
  • Strict Content Security Policy (CSP): Implement a restrictive Content Security Policy for the WebView to minimize the attack surface for XSS and limit the capabilities of injected Javascript, even if XSS occurs.
  • Regular Web Application Security Audits: Conduct frequent and thorough security audits and penetration testing of the web application to proactively identify and remediate XSS vulnerabilities before they can be exploited via the bridge.