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attack-surface.md

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Attack Surface Analysis for envoyproxy/envoy

Attack Surface: Insecure Admin Interface Exposure

  • Description: Envoy's built-in administrative interface, intended for local management and debugging, becomes a critical vulnerability if exposed without proper access controls.
  • Envoy Contribution: Envoy provides the admin interface as a core feature, directly introducing this attack surface if not secured.
  • Example: An Envoy instance deployed as a public-facing proxy has its admin interface (port 9901) accessible without authentication. Attackers can access /config_dump to reveal sensitive configuration, /server_shutdown to cause denial of service, or /runtime_modify to potentially alter Envoy's behavior.
  • Impact: Full compromise of Envoy proxy control, denial of service, information disclosure of sensitive configuration, potential for traffic manipulation.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Disable Admin Interface: If the admin interface is not essential for production public-facing Envoys, disable it using configuration options.
    • Restrict Access by IP: Configure Envoy to only allow admin interface access from trusted internal IP ranges using listener filters.
    • Implement Authentication: Enable authentication mechanisms (like RBAC or external auth) specifically for the admin interface listener.
    • Network Isolation: Ensure the network segment where the admin interface is accessible is strictly controlled and not publicly reachable.

Attack Surface: Misconfigured Role-Based Access Control (RBAC)

  • Description: Envoy's RBAC system, designed to control access to resources within Envoy itself, can be misconfigured to grant overly broad permissions, leading to unauthorized actions.
  • Envoy Contribution: Envoy implements RBAC as a security feature, but misconfiguration directly creates a vulnerability within Envoy's access control framework.
  • Example: An RBAC policy incorrectly grants READ access to the /config_dump endpoint to a broad group of users or services. An attacker compromising a low-privilege service within that group can then access sensitive Envoy configuration details.
  • Impact: Information disclosure of sensitive Envoy configuration, unauthorized access to Envoy management endpoints, potential for further exploitation based on exposed information.
  • Risk Severity: High
  • Mitigation Strategies:
    • Principle of Least Privilege: Design RBAC policies to grant the absolute minimum permissions necessary for each role or principal.
    • Regular RBAC Audits: Periodically review and audit RBAC policies to ensure they remain appropriate and secure as roles and requirements evolve.
    • Granular Policies: Define policies with specific actions and resources instead of using wildcard permissions wherever possible to limit scope.
    • Testing and Validation: Thoroughly test RBAC policies in a staging environment to verify they function as intended and prevent unintended access.

Attack Surface: Vulnerabilities in Custom Envoy Filters

  • Description: Custom Envoy filters, extending Envoy's functionality, can introduce vulnerabilities if they contain coding errors, logic flaws, or fail to handle inputs securely.
  • Envoy Contribution: Envoy's extensibility mechanism for custom filters allows for the introduction of third-party or internally developed code, which can contain vulnerabilities directly within the Envoy process.
  • Example: A custom filter designed for request modification has a buffer overflow vulnerability when processing oversized headers. An attacker crafts a request with an extremely large header, triggering the overflow and potentially achieving code execution within the Envoy process.
  • Impact: Code execution within Envoy, denial of service, bypass of security controls intended by the filter, potential data corruption or leakage depending on filter functionality.
  • Risk Severity: High to Critical (depending on vulnerability type and filter's role)
  • Mitigation Strategies:
    • Secure Filter Development Lifecycle: Implement a rigorous secure development lifecycle for custom filters, including threat modeling, secure coding practices, and code reviews.
    • Input Validation and Sanitization: Mandatory and thorough input validation and sanitization within custom filters to prevent injection attacks and other input-related vulnerabilities.
    • Memory Safety: Utilize memory-safe programming languages and practices when developing custom filters to minimize memory corruption risks.
    • Regular Security Audits: Conduct regular security audits and penetration testing specifically targeting custom filters.
    • Sandboxing (where applicable): Explore sandboxing technologies (like WebAssembly if supported for filters) to isolate custom filter execution and limit the impact of vulnerabilities.

Attack Surface: Insecure xDS Communication

  • Description: The communication channel between Envoy and its control plane (xDS server) is critical. If this channel is not secured, attackers can intercept or manipulate configuration updates, compromising Envoy's behavior.
  • Envoy Contribution: Envoy relies on xDS for dynamic configuration, making the security of the xDS channel a direct dependency for Envoy's operational security.
  • Example: xDS communication is configured without TLS encryption or mutual authentication. An attacker on the network performs a man-in-the-middle attack, intercepts xDS configuration updates, and injects malicious routing rules that redirect traffic to attacker-controlled servers or disrupt service.
  • Impact: Full compromise of Envoy configuration and routing, potential redirection of traffic, denial of service, data interception, and potential compromise of backend services.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Mandatory TLS for xDS: Always enforce TLS encryption for all xDS communication between Envoy and the control plane.
    • Mutual TLS (mTLS): Implement mutual TLS to authenticate both Envoy and the xDS server, ensuring only authorized components can participate in configuration updates.
    • Secure Control Plane Infrastructure: Harden the xDS server infrastructure itself and restrict access to it to authorized personnel and systems.
    • Configuration Validation on Control Plane: Implement robust validation and sanitization of configuration data on the xDS server before it is pushed to Envoy instances to prevent malicious configuration injection.
    • Network Segmentation: Isolate the control plane network from public networks and consider segmenting it from the data plane network for enhanced security.