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attack-surface.md

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Attack Surface Analysis for envoyproxy/envoy

Attack Surface: 1. Configuration Errors (General)

  • Description: Broad category encompassing any misconfiguration of Envoy's extensive settings, leading to unintended behavior and security vulnerabilities. This is the primary attack vector for Envoy.
    • How Envoy Contributes: Envoy's highly configurable nature, while powerful, increases the likelihood of human error and complex interactions between settings. The sheer number of configuration options makes this a high-risk area.
    • Example: A listener is accidentally configured to bind to 0.0.0.0 (all interfaces) instead of a specific internal IP address, exposing an internal service to the public internet. Another example: incorrect RBAC configuration allows unauthorized access to the admin interface.
    • Impact: Unauthorized access to internal services, data breaches, denial of service, complete system compromise.
    • Risk Severity: Critical to High (depending on the specific misconfiguration).
    • Mitigation Strategies:
      • Configuration Validation: Mandatory automated validation of Envoy configurations before deployment, using tools like envoy --mode validate or custom validation scripts. This is the single most important mitigation.
      • Principle of Least Privilege: Configure Envoy with the absolute minimum necessary permissions and access.
      • Infrastructure as Code (IaC): Manage Envoy configurations using IaC tools (e.g., Terraform, Ansible) to ensure consistency, repeatability, and auditability.
      • Regular Audits: Conduct frequent security audits of Envoy configurations, ideally automated.
      • Configuration Linting: Use linters specifically designed for Envoy configuration files to catch common errors and enforce best practices.
      • Change Management: Implement a strict change management process for any configuration modifications, including peer review and testing.

Attack Surface: 2. Listener Misconfiguration

  • Description: Incorrectly configured listeners, exposing services unintentionally or allowing unauthorized traffic. This is a direct consequence of Envoy's role as a proxy.
    • How Envoy Contributes: Envoy's listeners are the primary entry points for traffic; misconfiguration directly impacts what traffic is accepted and how it is handled.
    • Example: A listener intended for internal traffic is configured without proper TLS encryption or authentication (or with weak ciphers), allowing an attacker on the same network to eavesdrop or inject malicious traffic. Another example: missing or incorrect xff_num_trusted_hops configuration allows IP spoofing.
    • Impact: Exposure of internal services, man-in-the-middle attacks, data breaches, complete bypass of security controls.
    • Risk Severity: Critical to High
    • Mitigation Strategies:
      • Specific IP Binding: Bind listeners to specific internal IP addresses only. Avoid 0.0.0.0 unless absolutely necessary and with extremely strong justification and network-level controls.
      • Mandatory TLS: Enforce TLS encryption for all listeners, using strong ciphers and protocols (TLS 1.3 only if possible).
      • mTLS Authentication: Implement mutual TLS (mTLS) for authentication of clients connecting to all sensitive listeners. This is crucial for service meshes.
      • Network Policies: Use network policies (e.g., Kubernetes NetworkPolicies, firewall rules) to restrict access to Envoy's listeners at the network level, in addition to Envoy's internal controls.
      • Proper xff_num_trusted_hops: Configure this setting correctly to prevent IP spoofing attacks.

Attack Surface: 3. Filter Chain Exploits

  • Description: Vulnerabilities within Envoy's filters (especially custom filters) or incorrect filter ordering, leading to direct exploitation of the Envoy process.
    • How Envoy Contributes: Envoy's filter chain is a core component for request processing; vulnerabilities in filters can be directly exploited to compromise Envoy itself.
    • Example: A custom Lua filter used for request transformation has a buffer overflow vulnerability that allows an attacker to execute arbitrary code within the Envoy process. Another example: a faulty JWT validation filter allows bypassing authentication.
    • Impact: Remote code execution, denial of service, complete system compromise, data exfiltration.
    • Risk Severity: Critical to High
    • Mitigation Strategies:
      • Minimize Custom Filters: Strongly avoid custom filters unless absolutely necessary and there is no built-in alternative.
      • Secure Coding (Filters): If custom filters are unavoidable, follow secure coding practices rigorously. Use memory-safe languages if possible (e.g., WebAssembly instead of Lua). Extensive code review and security testing are mandatory.
      • Filter Ordering: Ensure filters are ordered correctly to enforce security policies (e.g., authentication filters before authorization filters, rate limiting before expensive operations). Document the filter chain logic clearly.
      • Regular Filter Updates: Keep Envoy and all its filters (including third-party filters) up-to-date to patch known vulnerabilities. This includes subscribing to security advisories.
      • Sandboxing: Explore and implement sandboxing techniques for custom filters (e.g., WebAssembly) to limit their impact if compromised. This is a crucial defense-in-depth measure.

Attack Surface: 4. Envoy CVEs (Known Vulnerabilities)

  • Description: Exploitation of publicly disclosed vulnerabilities in Envoy itself. This is an inherent risk with any software.
    • How Envoy Contributes: Envoy, as a complex piece of software, is susceptible to vulnerabilities. Its role as a network proxy makes it a high-value target.
    • Example: An attacker exploits a known remote code execution vulnerability in a specific Envoy version to gain control of the proxy and access the network.
    • Impact: Denial of service, remote code execution, information disclosure, complete network compromise (depending on the specific CVE).
    • Risk Severity: Critical to High (depending on the specific CVE).
    • Mitigation Strategies:
      • Vulnerability Management: Implement a robust vulnerability management program to track and remediate known vulnerabilities proactively.
      • Prompt Patching: Apply security patches and updates to Envoy immediately upon release. Automate this process where possible.
      • Monitoring: Monitor for suspicious activity that might indicate exploitation attempts, using both network and host-based monitoring.
      • WAF/IDS/IPS: Use a Web Application Firewall (WAF), Intrusion Detection System (IDS), or Intrusion Prevention System (IPS) to detect and block known exploit attempts, but do not rely on this as the primary defense.

Attack Surface: 5. gRPC-Specific Attacks

  • Description: Attacks targeting Envoy's gRPC handling capabilities, exploiting vulnerabilities in Envoy's gRPC-specific features.
    • How Envoy Contributes: Envoy provides specific features for gRPC, including bridging, transcoding, and gRPC-Web support. Vulnerabilities in these features are directly exploitable.
    • Example: An attacker sends a malformed gRPC message that exploits a vulnerability in Envoy's gRPC transcoding logic, leading to a crash or, potentially, remote code execution.
    • Impact: Denial of service, potential for code execution (depending on the vulnerability).
    • Risk Severity: High
    • Mitigation Strategies:
      • gRPC Library Updates: Keep Envoy's gRPC libraries up-to-date, as vulnerabilities are often found in underlying libraries.
      • Strict Configuration: Carefully configure gRPC-specific features, paying close attention to security settings and avoiding unnecessary features.
      • Message Validation: If possible, validate the contents of gRPC messages within Envoy to prevent malformed data from reaching backend services. This can be challenging but is a strong defense.
      • Input Sanitization: Sanitize any user-provided input that is used in gRPC communication, particularly if transcoding is involved.