Threat: Unintentional Native Function Exposure
* **Description:** An attacker crafts malicious JavaScript within the webview to call native functions that were not intended to be exposed. This relies on guessing function names or exploiting overly permissive registration (e.g., wildcards in `registerHandler`).
* **Impact:** Access to sensitive data (contacts, location, files), device control (camera, microphone), or execution of privileged operations, potentially leading to complete device compromise.
* **Affected Component:** `registerHandler` (and similar functions for registering native callbacks) in the bridge implementation. The overall bridge configuration and handler registration logic.
* **Risk Severity:** High to Critical (depending on the exposed functionality).
* **Mitigation Strategies:**
* **Strict Handler Registration:** Only register *absolutely essential* functions. *Never* use wildcards. Use explicit, descriptive names.
* **Input Validation:** Rigorously validate *all* input received from the webview in *every* native handler. Check types, lengths, and expected values. Assume all input is malicious.
* **Code Reviews:** Thoroughly review all bridge configuration and handler code, specifically looking for overly permissive registrations and missing input validation.
* **Documentation:** Maintain clear, up-to-date documentation of all exposed functions, their parameters, and their intended use.
Threat: Message Spoofing/Tampering (Command Injection)
* **Description:** An attacker intercepts and modifies messages sent from the *untrusted* webview to the native application. They inject malicious commands or alter data to trigger unintended actions on the native side. This is a direct attack on the bridge's communication channel.
* **Impact:** Execution of arbitrary native code (if input validation is weak or absent), data corruption, unauthorized actions, potentially leading to complete application or device compromise.
* **Affected Component:** The message passing mechanism itself (e.g., the `send` and `callHandler` functions, and the corresponding native message handling logic). The core of the bridge's functionality.
* **Risk Severity:** High to Critical (heavily dependent on the presence and quality of input validation).
* **Mitigation Strategies:**
* **Input Validation (Primary and Essential):** Assume *all* messages from the webview are potentially malicious. Strictly and comprehensively validate *all* data received in *every* native handler. This is the *most critical* mitigation.
* **Message Integrity (Secondary, Limited Usefulness):** If (and *only if*) the webview content is *fully trusted* (e.g., loaded from your own server over HTTPS and you control the entire content), *then* you could consider HMACs or digital signatures. However, this is *not* a reliable defense if the webview content is untrusted.
* **Sequence Numbers/Nonces:** Use to prevent replay attacks.
Threat: Bridge Implementation Vulnerability
* **Description:** The `webviewjavascriptbridge` library itself (or the specific bridge implementation being used) contains a security vulnerability (e.g., a buffer overflow, a logic flaw, a deserialization issue) that can be directly exploited by sending crafted messages through the bridge.
* **Impact:** Varies greatly depending on the specific vulnerability. Could range from denial of service to arbitrary code execution in the native context, potentially leading to complete system compromise.
* **Affected Component:** The entire bridge library itself; any part of the library's code could be vulnerable.
* **Risk Severity:** Variable (High to Critical, depending on the vulnerability). Assume Critical until proven otherwise.
* **Mitigation Strategies:**
* **Keep Updated:** Use the absolute latest version of the library, ensuring you receive security patches promptly.
* **Security Audits:** If feasible, conduct or commission security audits of the bridge library and its integration with your application.
* **Choose a Well-Maintained Library:** Select a library with a good security track record, active maintenance, and prompt response to reported vulnerabilities.
* **Vulnerability Scanning:** Use vulnerability scanning tools to check for known issues in the library.
Threat: Leaking of Secret Key Used for HMAC (If HMAC is Inappropriately Used)
* **Description:** If HMAC is used for message integrity *and* the secret key is leaked (e.g., hardcoded in JavaScript within the *untrusted* webview, exposed through a separate vulnerability), the attacker can forge valid messages, completely bypassing the HMAC protection. This highlights the *misuse* of HMAC in an untrusted context.
* **Impact:** Complete bypass of message integrity checks, leading to successful command injection and other attacks, effectively rendering the HMAC useless.
* **Affected Component:** The key management and storage for the HMAC secret. The message sending and verification logic within the bridge.
* **Risk Severity:** Critical (if HMAC is relied upon as the *primary* defense against message tampering with an *untrusted* webview).
* **Mitigation Strategies:**
* **Secure Key Storage:** *Never* store the secret key in the webview's JavaScript code or any other location accessible to the untrusted webview. This is a fundamental security principle.
* **Avoid HMAC with Untrusted Webviews:** *Do not use HMAC* to secure communication with *untrusted* webview content. It provides a false sense of security. Rely *entirely* on rigorous input validation on the native side.
* **Key Derivation (If applicable):** If the webview is *trusted*, derive the key dynamically from a more secure source.