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Project Design Document: Elasticsearch .NET Client (elasticsearch-net)

Document Version: 1.1 Date: 2023-10-27 Author: AI Expert

1. Introduction

This document provides a design overview of the Elasticsearch .NET Client (elasticsearch-net), the official .NET client for Elasticsearch. This document is intended to be used as a foundation for threat modeling activities and offers a detailed description of the client's architecture, components, data flow, and security considerations.

The elasticsearch-net client empowers .NET applications to interact seamlessly with Elasticsearch clusters, enabling core functionalities such as indexing, searching, and managing Elasticsearch data and cluster configurations. This document specifically focuses on the client library itself and its interaction with an Elasticsearch cluster, excluding the internal workings of Elasticsearch.

Project Repository: https://github.com/elastic/elasticsearch-net

2. System Architecture

The following diagram illustrates the high-level architecture of the Elasticsearch .NET Client and its interaction with an Elasticsearch cluster.

graph TB
    direction TB
    subgraph ".NET Application Environment"
        "DotNetApp"[" .NET Application "]
    end
    subgraph "Elasticsearch .NET Client Library"
        "ElasticsearchClient"[" Elasticsearch .NET Client Library "]
        "CoreClient"[" Core Client "]
        "Serialization"[" Serialization (JSON.NET / System.Text.Json) "]
        "QueryDSL"[" Query DSL "]
        "LowLevelClient"[" Low-Level Client "]
        subgraph "HTTP Layer"
            "HttpClient"[" HTTP Client (e.g., HttpClient) "]
        end
        "HighLevelClient"[" High-Level Client "]
        "ConnectionPool"[" Connection Pooling "]
        "Diagnostics"[" Diagnostics & Observability "]
    end
    subgraph "Elasticsearch Cluster Environment"
        "ElasticsearchCluster"[" Elasticsearch Cluster "]
        "ElasticsearchNode"[" Elasticsearch Node "]
    end
    subgraph "Network Boundary"
        "NetworkBoundary"[" Network "]
    end

    "DotNetApp" --> "ElasticsearchClient"
    "ElasticsearchClient" --> "CoreClient"
    "CoreClient" --> "Serialization"
    "CoreClient" --> "QueryDSL"
    "CoreClient" --> "LowLevelClient"
    "CoreClient" --> "HighLevelClient"
    "CoreClient" --> "ConnectionPool"
    "CoreClient" --> "Diagnostics"

    "LowLevelClient" --> "HttpClient"
    "HttpClient" --> "NetworkBoundary"
    "NetworkBoundary" --> "ElasticsearchCluster"
    "ElasticsearchCluster" --> "NetworkBoundary"
    "NetworkBoundary" --> "HttpClient"
    "HttpClient" --> "LowLevelClient"


    "ElasticsearchCluster" --> "ElasticsearchNode"
    "ElasticsearchNode" --> "ElasticsearchCluster"
Loading

Description of Components:

  • .NET Application Environment: Represents the environment where the user application, developed in .NET, resides and utilizes the Elasticsearch .NET Client library to interact with Elasticsearch.
  • Elasticsearch .NET Client Library: This is the core library under design consideration. It encapsulates all functionalities necessary for communication with an Elasticsearch cluster.
    • Core Client: The central orchestrator of the client library. It manages the client's lifecycle, configuration settings, and request dispatching, coordinating interactions between other components.
    • Serialization (JSON.NET / System.Text.Json): Responsible for converting .NET objects into JSON format for requests to Elasticsearch and vice versa for responses. It typically leverages either JSON.NET (Newtonsoft.Json) or the more recent System.Text.Json library, offering flexibility in JSON handling.
    • Query DSL: Provides a fluent, strongly-typed API in C# for constructing Elasticsearch queries. This abstraction simplifies query creation, moving away from manual JSON construction and enhancing developer experience and type safety.
    • Low-Level Client: Exposes the raw Elasticsearch REST API endpoints directly as methods within the .NET client. This offers fine-grained control over Elasticsearch operations, mirroring the HTTP API closely for advanced use cases.
      • HTTP Client (e.g., HttpClient): Represents the underlying HTTP client implementation used for network communication. This is typically HttpClient in modern .NET applications, handling the actual HTTP requests and responses.
    • High-Level Client: Built upon the Low-Level Client, it provides a more user-friendly, object-oriented API. It simplifies common Elasticsearch tasks and offers abstractions for key Elasticsearch concepts like indices, documents, and mappings, improving developer productivity for typical operations.
    • Connection Pooling: Manages a pool of persistent connections to Elasticsearch cluster nodes. It optimizes performance and resilience by handling connection establishment, reuse, and health checks, reducing connection overhead.
    • Diagnostics & Observability: Offers features for logging, tracing, and metrics collection to enable monitoring of the client's behavior and facilitate troubleshooting. This includes integration with standard .NET logging frameworks and potentially distributed tracing systems for deeper insights.
  • Network Boundary: Represents the network infrastructure facilitating communication between the .NET Client and the Elasticsearch Cluster. This could be a local network, a wide area network like the internet, or a cloud-based network.
  • Elasticsearch Cluster Environment: Represents the Elasticsearch cluster environment, composed of one or more Elasticsearch nodes.
    • Elasticsearch Node: An individual Elasticsearch server instance within the cluster, responsible for data storage and processing search and indexing requests.

3. Data Flow

The primary data flow involves communication between the .NET Application, the Elasticsearch .NET Client, and the Elasticsearch Cluster.

Request Flow (Application to Elasticsearch):

  1. The .NET Application initiates an Elasticsearch operation (e.g., indexing a document, executing a search query) using the Elasticsearch .NET Client API (either High-Level or Low-Level).
  2. The Elasticsearch .NET Client (specifically the Core Client and relevant components like QueryDSL or Serialization) processes the request based on the API used.
  3. The request is serialized into JSON format by the Serialization component, preparing it for network transmission.
  4. The Low-Level Client utilizes the ConnectionPool to efficiently obtain a healthy, reusable connection to an Elasticsearch node.
  5. The HttpClient sends the JSON request over the Network (typically via HTTPS for security or HTTP for development/testing) to the Elasticsearch Cluster.
  6. The Elasticsearch Cluster receives the request and processes it on an appropriate Elasticsearch Node.

Response Flow (Elasticsearch to Application):

  1. The Elasticsearch Cluster processes the request and generates a JSON response containing the result of the operation.
  2. The response is sent back over the Network to the HttpClient within the .NET Client.
  3. The HttpClient receives the response and passes it back to the Low-Level Client.
  4. The Serialization component deserializes the JSON response back into .NET objects, making the data accessible to the application.
  5. The Elasticsearch .NET Client returns the deserialized response data to the originating .NET Application.

Data Format:

  • Communication between the Elasticsearch .NET Client and the Elasticsearch Cluster is predominantly based on JSON (JavaScript Object Notation) for encoding both requests and responses due to its efficiency and widespread support.

Protocols:

  • The communication protocol is typically HTTP or, for secure communication, HTTPS. HTTPS is strongly recommended and should be enforced for production environments to guarantee data confidentiality and integrity during transit.

4. Security Considerations

Security is paramount for the Elasticsearch .NET Client and its interactions with Elasticsearch. The following outlines key security considerations, categorized for clarity and actionable threat modeling.

4.1. Transport Security (TLS/SSL) - Confidentiality, Integrity

  • Requirement: All communication between the .NET Client and the Elasticsearch Cluster must be encrypted using HTTPS (TLS/SSL) to protect data in transit.
  • Client Configuration: The client must be configurable to enforce HTTPS and to rigorously validate the Elasticsearch server's certificate to prevent man-in-the-middle attacks. Configuration options should include:
    • Enabling/Disabling TLS.
    • Specifying TLS versions (recommend TLS 1.2 or higher).
    • Certificate validation modes (full validation, certificate pinning).
    • Trust store configuration for custom certificates.
  • Threats Mitigated:
    • Eavesdropping (Information Disclosure): Prevents unauthorized interception and reading of sensitive data transmitted over the network.
    • Man-in-the-Middle (MITM) Attacks (Integrity, Confidentiality): Prevents attackers from intercepting and manipulating communication between the client and server.

4.2. Authentication - Authentication, Authorization

  • Requirement: The client must support a range of robust Elasticsearch authentication mechanisms to securely verify its identity to the cluster and ensure only authorized access.
  • Supported Mechanisms (Examples):
    • Basic Authentication (Username/Password): Credentials should never be hardcoded. Secure storage and retrieval are crucial, using environment variables, secure configuration stores, or secrets management systems.
      • Threat: Credential theft leading to unauthorized access.
      • Mitigation: Secure credential storage, password policies, rate limiting on authentication attempts.
    • API Keys: Elasticsearch API keys offer a more secure and auditable alternative to username/password. Client should provide seamless support for API key authentication.
      • Threat: API key compromise leading to unauthorized access.
      • Mitigation: Secure API key generation, rotation, and storage, principle of least privilege for key permissions.
    • Bearer Tokens (OAuth 2.0, JWT): Support for token-based authentication is essential for integration with modern identity providers (IdPs). Client should support configuring bearer token providers.
      • Threat: Token theft or expiration issues leading to access control problems.
      • Mitigation: Secure token handling, short-lived tokens, proper token validation.
    • Certificate-Based Authentication (Mutual TLS - mTLS): Using client certificates for mutual TLS provides strong, certificate-based authentication. Client should support configuring client certificates.
      • Threat: Private key compromise of client certificate.
      • Mitigation: Secure private key storage, certificate rotation, and revocation mechanisms.
  • Client Configuration: The client must provide clear and comprehensive configuration options for all supported authentication methods.
  • Threats Mitigated:
    • Spoofing (Authentication): Prevents unauthorized entities from impersonating legitimate clients.
    • Unauthorized Access (Authorization): Ensures only authenticated and authorized clients can interact with the Elasticsearch cluster.

4.3. Authorization - Authorization

  • Elasticsearch Responsibility: Authorization is primarily enforced by Elasticsearch's Role-Based Access Control (RBAC) and Security features within the cluster itself.
  • Client Role: The client's responsibility is to faithfully transmit the authenticated identity to Elasticsearch. The client itself does not implement or enforce authorization policies.
  • Consideration: It is crucial to ensure that the user or service account used by the .NET application is granted the minimum necessary permissions within Elasticsearch (Principle of Least Privilege) to perform its intended operations. Regularly review and audit Elasticsearch role assignments.
  • Threats Mitigated:
    • Elevation of Privilege (Authorization): Prevents clients from performing actions beyond their authorized roles and permissions within Elasticsearch.
    • Unauthorized Actions (Authorization): Restricts clients to only the operations they are explicitly permitted to perform.

4.4. Input Validation and Serialization - Integrity, Availability

  • Client-Side Validation: While Elasticsearch performs server-side validation, the client can and should implement client-side validation to catch common input errors early. This improves user experience and can prevent some classes of injection attacks by sanitizing or rejecting invalid input before it reaches Elasticsearch.
  • Serialization Security: The Serialization component (using JSON.NET or System.Text.Json) must be configured and used securely to prevent deserialization vulnerabilities.
    • Threat: Deserialization vulnerabilities leading to remote code execution or denial of service.
    • Mitigation: Use up-to-date serialization libraries, avoid deserializing untrusted data without validation, configure serialization settings to limit potential attack surface (e.g., type name handling).
  • Query DSL Security: While the Query DSL is designed to be safer than constructing raw JSON queries, developers should still avoid directly embedding untrusted user input into queries without proper sanitization or parameterization.
    • Threat: Elasticsearch Query DSL injection leading to data manipulation or information disclosure.
    • Mitigation: Parameterize queries, use input validation, and follow secure query building practices.
  • Threats Mitigated:
    • Tampering (Integrity): Prevents malicious modification of data sent to Elasticsearch.
    • Injection Attacks (Integrity, Availability, Confidentiality): Mitigates various injection attacks like Query DSL injection and JSON injection.
    • Denial of Service (Availability): Prevents malformed input from causing crashes or performance degradation.

4.5. Connection Pooling Security - Availability, Confidentiality, Integrity

  • Secure Connection Management: The ConnectionPool must securely manage connections, especially when authentication is involved. Connections should be properly closed and disposed of when no longer needed. Sensitive information should not be leaked through connection management.
  • Connection Hijacking: In shared network environments, the risk of connection hijacking should be considered. Enforcing HTTPS (TLS/SSL) is the primary mitigation for this.
  • Configuration Security: Connection pool settings (e.g., maximum connections, timeouts, idle connection timeouts) should be carefully configured to prevent resource exhaustion, denial-of-service scenarios, and to align with security best practices.
    • Threat: Connection hijacking, denial of service, resource exhaustion, information leakage through connection reuse.
    • Mitigation: Enforce HTTPS, configure appropriate connection pool limits and timeouts, regularly audit connection pool settings.
  • Threats Mitigated:
    • Denial of Service (Availability): Prevents connection pool misconfiguration from leading to service unavailability.
    • Confidentiality, Integrity: Mitigates risks associated with connection hijacking in insecure network environments (primarily through TLS).

4.6. Dependency Management - Integrity, Availability

  • Third-Party Libraries: The Elasticsearch .NET Client relies on external third-party libraries (e.g., JSON.NET/System.Text.Json, HTTP libraries, logging libraries).
  • Vulnerability Scanning: Regularly scan all dependencies for known security vulnerabilities using automated tools.
  • Dependency Updates: Promptly update to patched versions of dependencies when vulnerabilities are identified and patches are released.
  • Supply Chain Security: Ensure dependencies are obtained from trusted and verified sources to prevent supply chain attacks.
    • Threat: Exploitation of vulnerabilities in third-party libraries leading to various security breaches.
    • Mitigation: Regular vulnerability scanning, dependency updates, supply chain security practices.
  • Threats Mitigated:
    • Tampering (Integrity): Prevents compromised dependencies from introducing malicious code.
    • Denial of Service (Availability): Prevents vulnerabilities in dependencies from causing service disruptions.
    • Information Disclosure, Elevation of Privilege, etc.: Depending on the nature of the vulnerability in the dependency.

4.7. Logging and Diagnostics - Confidentiality, Integrity

  • Secure Logging: Logs should be carefully reviewed to ensure they do not inadvertently expose sensitive information such as passwords, API keys, personally identifiable information (PII), or internal system details that could aid attackers.
  • Log Injection: Be aware of potential log injection vulnerabilities if log messages are constructed using untrusted input. Sanitize or encode user-provided data before including it in logs.
    • Threat: Information disclosure through logs, log injection attacks leading to log manipulation or denial of service.
    • Mitigation: Secure logging practices, avoid logging sensitive data, sanitize log inputs, implement log monitoring and alerting.
  • Threats Mitigated:
    • Information Disclosure (Confidentiality): Prevents sensitive data from being exposed in logs.
    • Tampering (Integrity): Prevents log manipulation through log injection.

4.8. Configuration Management - Confidentiality, Integrity, Availability

  • Secure Storage of Credentials: Connection strings, usernames, passwords, API keys, certificates, and other sensitive configuration data must be stored securely. Avoid storing them in plain text in configuration files or code.
    • Recommended Practices:
      • Environment Variables: Use environment variables for configuration, especially in containerized environments.
      • Secrets Management Systems: Integrate with dedicated secrets management systems like Azure Key Vault, HashiCorp Vault, AWS Secrets Manager, etc.
      • Secure Configuration Files: If configuration files are used, ensure they are encrypted at rest and access is strictly controlled using file system permissions.
  • Avoid Hardcoding Secrets: Never hardcode sensitive credentials directly within the application code.
  • Principle of Least Privilege: Grant only the necessary permissions to the application's service account or user accessing configuration resources.
  • Configuration Validation: Implement validation of configuration settings at startup to detect misconfigurations early.
    • Threat: Exposure of sensitive credentials, unauthorized access due to compromised credentials or misconfigurations, service disruption due to incorrect configuration.
    • Mitigation: Secure credential storage, avoid hardcoding secrets, principle of least privilege, configuration validation, regular security audits of configuration practices.
  • Threats Mitigated:
    • Spoofing, Elevation of Privilege, Information Disclosure, etc.: Consequences of compromised credentials or insecure configurations can be wide-ranging.
    • Denial of Service (Availability): Misconfigurations can lead to service outages.

5. Threat Modeling Focus Areas (STRIDE Based)

To facilitate structured threat modeling, the following areas are categorized using the STRIDE model (Spoofing, Tampering, Repudiation, Information Disclosure, Denial of Service, Elevation of Privilege). This provides a framework for systematically identifying potential threats.

  1. Spoofing (Authentication Bypass):

    • Weak or default authentication configurations.
    • Vulnerabilities in authentication mechanism implementations within the client.
    • Lack of mutual authentication (mTLS) where required.
    • Exploitation of session management flaws (if applicable at client level).

  2. Tampering (Integrity Violations):

    • Elasticsearch Query DSL injection vulnerabilities allowing malicious query modification.
    • JSON injection vulnerabilities during serialization/deserialization leading to data corruption.
    • Man-in-the-Middle attacks if TLS is not properly enforced, allowing data modification in transit.
    • Log injection attacks leading to log data manipulation.

  3. Repudiation (Non-Accountability):

    • Insufficient logging of client actions for auditing and accountability.
    • Lack of traceability of requests back to originating applications or users.

  4. Information Disclosure (Confidentiality Breaches):

    • Exposure of sensitive data in logs (credentials, PII, internal details).
    • Information leakage through verbose error messages or overly detailed responses.
    • Data interception due to lack of TLS encryption.
    • Deserialization vulnerabilities potentially exposing internal data structures.
    • Exposure of sensitive configuration data (credentials, connection strings) due to insecure storage.

  5. Denial of Service (Availability Impacts):

    • Maliciously crafted queries designed to overload the Elasticsearch cluster.
    • Resource exhaustion in the client due to connection pool misconfiguration or handling of malicious responses.
    • Vulnerabilities in dependency libraries leading to crashes or performance degradation.
    • Misconfigured connection pool settings leading to connection exhaustion.

  6. Elevation of Privilege (Authorization Failures):

    • Exploitation of authorization vulnerabilities in Elasticsearch due to client misconfiguration or improper role assignments.
    • Credential compromise leading to unauthorized access with elevated privileges.

By focusing threat modeling efforts on these STRIDE-categorized areas, a comprehensive security assessment of the Elasticsearch .NET Client and its integration within a .NET application can be effectively conducted. This document provides a solid foundation for more in-depth threat modeling exercises, such as utilizing STRIDE, PASTA, or other suitable methodologies. Remember to consider the specific context of your application and deployment environment during threat modeling.