Attack Surface: Path Traversal via Handlers
Description: Attackers manipulate file paths within requests to access files outside the intended directory. This exploits vulnerabilities in how a developer's handler code uses GCDWebServer's request processing.
GCDWebServer Contribution: GCDWebServer provides the mechanism for handlers to access the request path and associated data (query parameters, etc.). It does not inherently validate or sanitize this data; that is the responsibility of the handler code written by the developer using the library. The library facilitates the possibility of the vulnerability, but the vulnerability itself exists in the application's handler.
Example: A handler uses request.query["filename"] directly to open a file, without any checks. An attacker provides filename=../../etc/passwd.
Impact: Unauthorized access to sensitive files, potentially leading to system compromise.
Risk Severity: Critical
Mitigation Strategies:
* Strict Input Validation: Validate and sanitize all parts of the request used to construct file paths within the handler. Reject any input containing suspicious characters (e.g., "../", "/", control characters).
* Whitelist Allowed Paths/Filenames: Maintain a whitelist of allowed file names or paths, and reject any request that doesn't match the whitelist. This is far more secure than trying to blacklist dangerous characters.
* Safe Base Directory: Construct file paths by combining a known, safe base directory with the sanitized user input. Never use user-provided input directly as the full file path.
* Canonicalization: Before accessing a file, canonicalize the path to resolve any symbolic links or relative path components.
Attack Surface: Handler Logic Errors (Authentication/Authorization Bypass)
Description: Flaws in the authentication, authorization, or session management logic within a GCDWebServer handler allow attackers to bypass security controls.
GCDWebServer Contribution: GCDWebServer provides the framework for developers to implement these security mechanisms within their handlers. The library itself does not provide built-in authentication or authorization; it's the developer's responsibility to implement these correctly using the handler's request and response objects. The vulnerability lies in the application's handler code, not the library itself, but the library provides the context in which the handler operates.
Example: A handler checks for a cookie named "admin" but doesn't verify its signature or origin, allowing an attacker to set a fake "admin" cookie.
Impact: Unauthorized access to sensitive functionality or data, potentially leading to complete application compromise.
Risk Severity: High to Critical (depending on the protected resource)
Mitigation Strategies:
* Use Established Security Libraries: Leverage well-vetted authentication and authorization libraries instead of implementing these mechanisms from scratch within the handler.
* Centralized Security Logic: Implement security checks in a centralized and consistent manner, rather than scattering them throughout individual handlers.
* Secure Session Management: Use secure, randomly generated session identifiers, and handle session data securely (e.g., server-side storage, proper expiration).
* Input Validation (Always): Validate all input within the handler, even for authenticated users, to prevent other vulnerabilities.
* Thorough Testing: Rigorously test authentication and authorization logic, including edge cases and negative scenarios.
Attack Surface: Resource Exhaustion (DoS) via Handler Abuse
Description: Attackers exploit handlers designed for resource-intensive operations to cause denial of service by consuming excessive server resources.
GCDWebServer Contribution: GCDWebServer provides the environment in which handlers execute. It does not automatically limit the resources a handler can consume. The developer must implement resource limits and safeguards within the handler code. The library provides the concurrency model (GCD), which, if misused, can exacerbate resource exhaustion issues.
Example: A handler allows file uploads but doesn't limit the file size. An attacker uploads a massive file, consuming all available disk space or memory.
Impact: Denial of service, preventing legitimate users from accessing the application.
Risk Severity: High
Mitigation Strategies:
* Request Body Size Limits: Enforce strict limits on the size of request bodies within the handler, especially for file uploads.
* Timeouts: Set timeouts for handler operations to prevent long-running requests from blocking resources indefinitely.
* Rate Limiting: Limit the rate at which clients can call specific handlers, particularly those known to be resource-intensive.
* Resource Monitoring: Monitor server resource usage and implement alerts for unusual activity.
* Careful Asynchronous Task Management: Use GCD responsibly within handlers. Avoid creating an unbounded number of asynchronous tasks, which could lead to resource exhaustion.
* Input Validation: Validate input to prevent excessively large or complex data from being processed.
Attack Surface: Unintended Handler Exposure
Description: Handlers intended for internal use are accidentally exposed publicly due to misconfiguration of routes within the GCDWebServer setup.
GCDWebServer Contribution: GCDWebServer allows developers to define the routes and associate them with handlers. The vulnerability arises from incorrectly defining these routes, exposing handlers that should be protected. The library provides the routing mechanism, but the developer is responsible for using it securely.
Example: A handler for administrative functions is registered at /admin without any authentication checks, making it accessible to anyone.
Impact: Unauthorized access to sensitive functionality or data.
Risk Severity: High to Critical (depending on the exposed functionality)
Mitigation Strategies:
* Careful Route Configuration: Meticulously review and double-check the paths for which handlers are registered. Use a clear and consistent naming convention to differentiate between public and internal routes.
* Code Review: Conduct thorough code reviews, specifically focusing on the code that registers handlers with GCDWebServer.
* Automated Testing: Implement automated tests to verify that sensitive routes are not accessible without proper authentication.
* Centralized Route Management: If feasible, manage all route registrations in a single, centralized location to simplify review and auditing.