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AdGuard Home Deep Security Analysis

1. Objective, Scope, and Methodology

Objective:

The objective of this deep analysis is to conduct a thorough security assessment of AdGuard Home, focusing on its key components, architecture, data flow, and deployment model. The analysis aims to identify potential security vulnerabilities, assess their impact, and propose actionable mitigation strategies. The primary goal is to enhance the security posture of AdGuard Home and protect its users from potential threats. This includes a specific focus on:

  • DNS Resolution Integrity: Ensuring the accuracy and reliability of DNS resolution, preventing manipulation or poisoning.
  • Filtering Effectiveness: Maintaining the effectiveness of ad and tracking blocking capabilities.
  • Web Interface Security: Protecting the management interface from unauthorized access and attacks.
  • Data Protection: Safeguarding sensitive data, particularly DNS query logs.
  • Deployment Security: Ensuring secure deployment and configuration, especially in the recommended Docker environment.
  • Build Process Security: Verifying the integrity and security of the build pipeline.

Scope:

This analysis covers the following aspects of AdGuard Home:

  • Core Functionality: DNS proxy, filtering engine, DNSSEC validation, HTTPS filtering (optional).
  • Web Interface: Authentication, authorization, input validation, session management.
  • Configuration: Storage, access control, data validation.
  • Data Handling: DNS query logs, statistics data.
  • Deployment: Docker containerization, network configuration, port mapping.
  • Build Process: GitHub Actions workflow, dependency management, static analysis, testing.
  • Upstream DNS Server Interaction: Security implications of using external DNS resolvers.

Methodology:

This analysis employs the following methodologies:

  1. Security Design Review Analysis: Thorough examination of the provided security design review document, including business posture, security posture, C4 diagrams, deployment model, and build process.
  2. Codebase Review (Inferred): Based on the provided information and publicly available documentation, we will infer the likely structure and behavior of the codebase. Since direct access to the codebase is not provided, this will be a high-level analysis based on the project's description and known functionalities.
  3. Threat Modeling: Identification of potential threats and attack vectors based on the system's architecture and functionality.
  4. Vulnerability Assessment: Assessment of potential vulnerabilities based on identified threats and known security weaknesses.
  5. Mitigation Strategy Recommendation: Proposal of actionable and tailored mitigation strategies to address identified vulnerabilities.
  6. Best Practices Review: Comparison of AdGuard Home's security controls against industry best practices.

2. Security Implications of Key Components

This section breaks down the security implications of each key component identified in the security design review and C4 diagrams.

2.1 Core Functionality

  • DNS Proxy:
    • Security Implications: The DNS proxy is the entry point for all DNS requests, making it a critical target for attacks. Vulnerabilities could allow attackers to intercept, modify, or redirect DNS traffic, leading to phishing, man-in-the-middle attacks, or denial-of-service. Rate limiting is crucial here.
    • Specific Recommendations: Ensure robust handling of malformed DNS packets. Implement strict size limits on DNS requests and responses. Validate all data received from upstream servers. Monitor for unusual DNS query patterns that might indicate an attack. Implement DNS over TLS (DoT) or DNS over HTTPS (DoH) to upstream servers, and consider offering these as options from clients.
  • Filtering Engine:
    • Security Implications: The filtering engine's effectiveness depends on the quality and maintenance of blocklists and the correctness of regular expressions. Poorly crafted regular expressions can lead to ReDoS vulnerabilities. Outdated blocklists can result in false negatives (allowing malicious domains) and false positives (blocking legitimate domains).
    • Specific Recommendations: Implement robust validation and sanitization of regular expressions used in filtering rules. Use a library or engine that is specifically designed to mitigate ReDoS attacks. Provide a mechanism for users to easily report false positives and false negatives. Regularly update blocklists from trusted sources. Implement a mechanism to verify the integrity of downloaded blocklists (e.g., checksums or signatures). Consider allowing users to choose from multiple blocklist providers.
  • DNSSEC Validation:
    • Security Implications: DNSSEC helps prevent DNS spoofing and cache poisoning attacks. Incorrect implementation or disabling DNSSEC can expose users to these risks.
    • Specific Recommendations: Ensure DNSSEC is enabled by default. Provide clear warnings to users if DNSSEC validation fails. Regularly test the DNSSEC implementation against known test vectors. Monitor for DNSSEC validation errors.
  • HTTPS Filtering (Optional):
    • Security Implications: This feature requires installing a custom root certificate, which creates a significant trust dependency. If the AdGuard Home server is compromised, the attacker could intercept and decrypt all HTTPS traffic from clients that have installed the certificate. This is a significant accepted risk.
    • Specific Recommendations: Provide very clear and prominent warnings to users about the risks of enabling HTTPS filtering. Document the security implications in detail. Consider providing alternative methods for HTTPS filtering that do not require a custom root certificate (e.g., using SNI filtering, although this is less effective). If a custom root certificate is used, ensure it is generated with strong cryptographic parameters and stored securely. Implement strict access controls to prevent unauthorized access to the private key associated with the root certificate. Consider using a Hardware Security Module (HSM) to protect the private key. Provide a mechanism for users to easily revoke the custom root certificate.

2.2 Web Interface

  • Authentication:
    • Security Implications: Weak authentication mechanisms can allow attackers to gain unauthorized access to the web interface and modify configuration settings, potentially compromising the entire network.
    • Specific Recommendations: Enforce strong password policies (minimum length, complexity requirements). Store passwords securely using a strong, adaptive hashing algorithm (e.g., Argon2, bcrypt). Implement account lockout mechanisms to prevent brute-force attacks. Strongly recommend implementing 2FA. Use a well-vetted authentication library.
  • Authorization:
    • Security Implications: Insufficient authorization controls can allow users to access or modify settings they should not have access to.
    • Specific Recommendations: Implement role-based access control (RBAC) with granular permissions. Apply the principle of least privilege. Ensure that all sensitive operations require appropriate authorization checks.
  • Input Validation:
    • Security Implications: Lack of input validation can lead to various injection attacks, including cross-site scripting (XSS), command injection, and SQL injection (if a database is used).
    • Specific Recommendations: Implement strict input validation for all user-provided data, including form inputs, URL parameters, and API requests. Use a whitelist approach, allowing only known-good characters and patterns. Sanitize all user input before using it in any context (e.g., displaying it in the web interface, using it in database queries, or executing system commands). Implement output encoding to prevent XSS attacks. Use parameterized queries or prepared statements to prevent SQL injection.
  • Session Management:
    • Security Implications: Poor session management can allow attackers to hijack user sessions and gain unauthorized access to the web interface.
    • Specific Recommendations: Use a secure session management library. Generate strong, random session IDs. Set the HttpOnly and Secure flags on session cookies. Implement session timeouts. Provide a mechanism for users to log out and invalidate their sessions. Consider using session tokens that are bound to the user's IP address or other identifying information to prevent session hijacking.

2.3 Configuration

  • Storage:
    • Security Implications: Insecure storage of configuration data can expose sensitive information, such as passwords, API keys, and custom filtering rules.
    • Specific Recommendations: Store sensitive configuration data securely. Encrypt sensitive data at rest. Implement strict access controls to the configuration file or database. Regularly back up the configuration data.
  • Access Control:
    • Security Implications: Insufficient access controls to the configuration can allow unauthorized users or processes to modify settings.
    • Specific Recommendations: Restrict access to the configuration file or database to only authorized users and processes. Use file system permissions or database privileges to enforce access control.
  • Data Validation:
    • Security Implications: Invalid configuration data can lead to unexpected behavior or vulnerabilities.
    • Specific Recommendations: Validate all configuration data before applying it. Ensure that configuration values are within expected ranges and conform to expected formats. Provide clear error messages to users if configuration data is invalid.

2.4 Data Handling

  • DNS Query Logs:
    • Security Implications: DNS query logs contain sensitive information about user browsing activity. Unauthorized access to these logs can compromise user privacy. Long-term storage of logs increases the risk of data breaches.
    • Specific Recommendations: Minimize the amount of data logged. Consider anonymizing or pseudonymizing DNS query logs. Implement strict access controls to the logs. Encrypt logs at rest. Implement a data retention policy that limits the amount of time logs are stored. Provide users with clear information about the logging practices and their privacy implications. Allow users to disable logging or configure the level of detail logged. Consider using a privacy-preserving logging mechanism, such as differential privacy.
  • Statistics Data:
    • Security Implications: While less sensitive than query logs, statistics data can still reveal information about user activity.
    • Specific Recommendations: Implement access controls to the statistics data. Consider aggregating statistics data to reduce the level of detail. Avoid storing any personally identifiable information (PII) in the statistics data.

2.5 Deployment (Docker Container)

  • Container Isolation:
    • Security Implications: Docker containers provide a degree of isolation, but vulnerabilities in the Docker engine or misconfiguration can allow attackers to escape the container and gain access to the host system.
    • Specific Recommendations: Use the latest stable version of Docker. Keep the Docker host operating system up-to-date with security patches. Run the AdGuard Home container with the least privileges necessary (e.g., do not run as root). Use a non-root user inside the container. Limit the container's capabilities using Docker security profiles (e.g., AppArmor, SELinux). Use a minimal base image for the container. Regularly scan the container image for vulnerabilities.
  • Network Configuration:
    • Security Implications: Incorrect network configuration can expose the AdGuard Home service to unauthorized access or allow attackers to intercept network traffic.
    • Specific Recommendations: Use a firewall to restrict access to the AdGuard Home container's ports (53, 80, 443). Only expose the necessary ports. Use a reverse proxy (e.g., Nginx, Traefik) to handle HTTPS traffic and provide additional security features (e.g., TLS termination, rate limiting, request filtering). Configure the reverse proxy to use strong TLS protocols and ciphers. Avoid exposing the AdGuard Home web interface directly to the internet. If remote access is required, use a VPN or other secure tunnel.
  • Port Mapping:
    • Security Implications: Incorrect port mapping can expose unintended services or allow attackers to bypass security controls.
    • Specific Recommendations: Carefully review and configure port mappings. Only map the necessary ports. Avoid using default ports if possible. Use a firewall to control access to mapped ports.
  • Volumes:
    • Security Implications: Data stored in volumes is persistent, even if the container is deleted. Insecurely configured volumes can expose sensitive data.
    • Specific Recommendations: Restrict access to volumes to only authorized users and processes. Use file system permissions to enforce access control. Encrypt sensitive data stored in volumes. Regularly back up volume data.

2.6 Build Process

  • Automated Build:
    • Security Implications: Automation reduces the risk of manual errors, but vulnerabilities in the build system or dependencies can compromise the build process.
    • Specific Recommendations: Use a trusted build system (GitHub Actions). Regularly update the build system and its dependencies. Verify the integrity of downloaded dependencies (e.g., using checksums or signatures).
  • Version Control:
    • Security Implications: Version control provides a history of changes, but unauthorized access to the repository can allow attackers to inject malicious code.
    • Specific Recommendations: Protect the GitHub repository with strong access controls. Require multi-factor authentication for all contributors. Use code review to ensure that all changes are reviewed and approved before being merged.
  • Dependency Management:
    • Security Implications: Vulnerabilities in dependencies can be exploited to compromise the application.
    • Specific Recommendations: Use a dependency management tool (Go modules) to track and version dependencies. Regularly update dependencies to the latest stable versions. Use a vulnerability scanner to identify known vulnerabilities in dependencies. Consider using a software composition analysis (SCA) tool to manage and track dependencies.
  • Static Analysis:
    • Security Implications: Static analysis can identify potential code quality and security issues, but it may not catch all vulnerabilities.
    • Specific Recommendations: Use a combination of linters and SAST tools. Configure the tools to use a comprehensive set of rules. Regularly review and address the findings of static analysis.
  • Automated Testing:
    • Security Implications: Automated testing can verify the functionality and security of the code, but it may not cover all possible scenarios.
    • Specific Recommendations: Write comprehensive unit and integration tests. Include security-focused tests (e.g., testing for input validation vulnerabilities, authentication bypass, authorization flaws). Use a code coverage tool to measure the effectiveness of the tests.
  • Signed Releases:
    • Security Implications: Signed releases help ensure the authenticity and integrity of the software, but the signing key must be protected.
    • Specific Recommendations: Sign all releases with a strong cryptographic key. Protect the private key securely. Publish the public key so that users can verify the signatures. Use a secure key management system. Verify that this is currently implemented.
  • Docker Image Build:
    • Security Implications: The Docker image build process can introduce vulnerabilities if not properly secured.
    • Specific Recommendations: Use a minimal base image (e.g., Alpine Linux). Verify that this is currently implemented. Avoid installing unnecessary packages. Regularly scan the Docker image for vulnerabilities. Use a secure registry to store and distribute the Docker image.
  • Minimal Base Image:
    • Security Implications: Reduces attack surface.
    • Specific Recommendations: Verify that this is currently implemented.

3. Threat Modeling and Vulnerability Assessment

This section identifies potential threats and vulnerabilities based on the architecture and functionality of AdGuard Home.

| Threat | Attack Vector | Vulnerability