sec-design-deep-analysis.md

Okay, let's perform a deep security analysis of the nginx-rtmp-module based on the provided security design review.

1. Objective, Scope, and Methodology

• Objective: To conduct a thorough security analysis of the key components of the nginx-rtmp-module, identifying potential vulnerabilities, weaknesses, and areas for security improvement. This analysis will focus on the module's code, configuration options, and interactions with external systems, as described in the design review. The goal is to provide actionable recommendations to enhance the module's security posture.

• Scope: The analysis will cover the following aspects of the nginx-rtmp-module:

  • Core RTMP protocol handling (ngx_rtmp_core_module.c).
  • Access control mechanisms (ngx_rtmp_access_module.c).
  • Authentication and notification features (ngx_rtmp_notify_module.c).
  • Execution of external programs (ngx_rtmp_exec_module.c).
  • Secure link functionality (ngx_rtmp_core_module.c).
  • Interaction with Nginx core.
  • Deployment and build process considerations.
  • Data flow and component interactions.

• Methodology:

  1. Architecture and Data Flow Review: Analyze the provided C4 diagrams and descriptions to understand the system's architecture, components, data flow, and trust boundaries.
  2. Codebase Inference: Based on the provided security design review, and the file names mentioned (e.g., ngx_rtmp_core_module.c), infer the likely functionality and potential security implications of the code. Since we don't have direct access to the codebase, we'll rely on the design review's description and common RTMP/Nginx module patterns.
  3. Threat Modeling: Identify potential threats based on the architecture, data flow, and inferred functionality. We'll consider common attack vectors against streaming servers and web applications.
  4. Vulnerability Analysis: Analyze each component and feature for potential vulnerabilities, considering the identified threats.
  5. Mitigation Recommendations: Propose specific and actionable mitigation strategies for each identified vulnerability or weakness. These recommendations will be tailored to the nginx-rtmp-module and its context.

2. Security Implications of Key Components

Let's break down the security implications of each key component, drawing inferences from the design review:

• ngx_rtmp_core_module.c (Core RTMP Handling & Secure Link):

  • Functionality (Inferred): This module likely handles the core RTMP protocol parsing, message handling, connection management, and stream multiplexing. It also implements the "secure link" feature.
  • Security Implications:
    • Protocol Parsing Vulnerabilities: RTMP is a complex protocol. Bugs in parsing RTMP messages (e.g., chunk handling, AMF parsing) could lead to buffer overflows, denial-of-service (DoS), or potentially remote code execution (RCE). Fuzzing the RTMP input is crucial.
    • Secure Link Implementation Flaws: The secure link feature relies on a shared secret and time-based tokens. Weaknesses in the token generation algorithm, insufficient entropy in the secret, or improper time validation could allow attackers to bypass access controls and access streams without authorization. Predictable tokens are a major risk.
    • Replay Attacks (Secure Link): If the secure link implementation doesn't properly handle replay attacks, an attacker could capture a valid URL and reuse it multiple times, even after it should have expired. Nonces or strict time window checks are needed.
    • Referrer Validation Weaknesses: If the SWF URL (referrer) validation is implemented incorrectly, it could be bypassed by attackers using techniques like referrer spoofing. Strict URL parsing and validation are essential.
    • Denial of Service (DoS): The core module is likely susceptible to various DoS attacks, such as slowloris, connection exhaustion, or resource exhaustion attacks targeting RTMP-specific features.

• ngx_rtmp_access_module.c (Access Control):

  • Functionality (Inferred): This module implements IP-based access control using allow and deny directives.
  • Security Implications:
    • IP Spoofing: IP-based access control is inherently vulnerable to IP spoofing attacks. An attacker could forge the source IP address of a trusted client to bypass restrictions. This is particularly relevant if the server is behind a reverse proxy or load balancer that doesn't properly validate the original client IP (e.g., using X-Forwarded-For).
    • Limited Granularity: IP-based access control offers limited granularity. It cannot distinguish between different users on the same IP address (e.g., behind a NAT).
    • Configuration Errors: Misconfiguration of allow and deny directives can lead to unintended access or denial of service.

• ngx_rtmp_notify_module.c (Authentication & Notifications):

  • Functionality (Inferred): This module handles on_connect authentication and likely other notification events (e.g., on_publish, on_play). It interacts with external control applications.
  • Security Implications:
    • External Application Security: The security of the authentication process heavily relies on the security of the external control application. Vulnerabilities in the external application (e.g., SQL injection, command injection, authentication bypass) can compromise the entire streaming server.
    • Communication Security: The communication between the nginx-rtmp-module and the external control application must be secured. If the communication is unencrypted or uses weak authentication, an attacker could intercept credentials or manipulate authentication decisions.
    • Input Validation (to External App): The module must carefully validate any data passed to the external control application to prevent injection attacks.
    • Denial of Service (DoS): A slow or unresponsive external authentication application can cause a DoS for the streaming server, as new connections will be blocked until authentication completes.

• ngx_rtmp_exec_module.c (Execution of External Programs):

  • Functionality (Inferred): This module allows executing external programs on certain events (e.g., publish, play).
  • Security Implications:
    • Command Injection: This is the most significant risk. If any user-supplied data (e.g., stream name, client IP) is passed to the external program without proper sanitization and escaping, an attacker could inject arbitrary commands, leading to RCE. This is a critical vulnerability.
    • Privilege Escalation: If the external program runs with elevated privileges (e.g., as root), a command injection vulnerability could allow an attacker to gain full control of the server.
    • Resource Exhaustion: An attacker could trigger the execution of resource-intensive external programs repeatedly, leading to a DoS.
    • Information Disclosure: Errors or output from the external program could leak sensitive information.

• Nginx Core Security:

  • Functionality (Inferred): The nginx-rtmp-module relies on the underlying Nginx web server for core functionality like network handling, process management, and configuration parsing.
  • Security Implications:
    • Nginx Vulnerabilities: Vulnerabilities in Nginx itself can affect the RTMP module. Keeping Nginx up-to-date is crucial.
    • Configuration Hardening: The overall security of the system depends on the secure configuration of Nginx (e.g., disabling unnecessary modules, restricting file system access).
    • Resource Limits: Nginx's resource limits (e.g., worker connections, memory limits) can help mitigate DoS attacks.

3. Architecture, Components, and Data Flow (Inferred)

Based on the C4 diagrams and descriptions, we can infer the following:

• Architecture: The system is built as a module that extends the Nginx web server. Nginx acts as the primary entry point for client connections, handling both HTTP and RTMP traffic. The RTMP module processes RTMP-specific requests. External services (authentication, recording, monitoring) are integrated.
• Components:
  • Nginx Web Server: The core web server.
  • RTMP Module: The nginx-rtmp-module itself, containing sub-modules for specific functionality (access control, authentication, etc.).
  • External Authentication Service: An optional service for user authentication and authorization.
  • Recording Storage: Storage for recorded streams.
  • Monitoring System: A system for monitoring performance and health.
  • CDNs: Content Delivery Networks for stream distribution.
• Data Flow:
  1. A client initiates an RTMP connection to the Nginx server.
  2. Nginx receives the connection and passes it to the RTMP module.
  3. The RTMP module parses the RTMP messages.
  4. For authentication, the RTMP module may communicate with an external authentication service.
  5. Access control checks (IP-based or secure link) are performed.
  6. If the connection is allowed, the RTMP module handles the stream (receiving or sending data).
  7. The RTMP module may interact with the recording storage to save the stream.
  8. The RTMP module may send metrics and logs to the monitoring system.
  9. The RTMP module may interact with CDNs to distribute the stream.

4. Specific Security Considerations and Mitigation Strategies

Here's a table summarizing specific security considerations and tailored mitigation strategies:

| Component | Threat | Vulnerability | Mitigation Strategy

| Component | Threat | Vulnerability | Mitigation Strategy