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Mitigation Strategies Analysis for fatedier/frp

Mitigation Strategy: Enable Token-Based Authentication for frp Server

  • Description:

    1. Generate a strong, unique token: Use a cryptographically secure random number generator to create a long, complex token string. Avoid using easily guessable tokens.
    2. Configure token in frps.ini: Open the frp server configuration file (frps.ini) and locate the [common] section. Add or modify the line token = your_strong_token_here, replacing your_strong_token_here with the generated token.
    3. Configure token in frpc.ini on all clients: For each frp client configuration file (frpc.ini), locate the [common] section and add or modify the line token = your_strong_token_here, using the same token configured on the server.
    4. Restart frp server and clients: Restart the frp server and all frp clients for the configuration changes to take effect.

    • Threats Mitigated:

      • Unauthorized Server Access (High Severity): Without token authentication, anyone who can reach the frp server port can potentially connect as a client and establish tunnels, gaining unauthorized access to internal services via frp.
      • Brute-Force Attacks on frp Authentication (Medium Severity): An open frp server without token authentication is more vulnerable to brute-force attempts to guess client connection parameters.

    • Impact:

      • Unauthorized Server Access: Significant reduction in risk of unauthorized frp client connections. Token authentication makes it extremely difficult for unauthorized clients to connect to the frp server.
      • Brute-Force Attacks on frp Authentication: Moderate reduction in risk. While token guessing is still theoretically possible, the complexity of strong tokens makes it practically infeasible.

    • Currently Implemented: Partially implemented. Token authentication is enabled on the production frp server, but not consistently enforced on all development and testing client configurations.

    • Missing Implementation:

      • Enforce token authentication on all development and testing frp client configurations.
      • Implement automated token generation and secure distribution mechanism for new frp clients.

Mitigation Strategy: Implement TLS Encryption for frp Communication

  • Description:

    1. Obtain TLS certificates: Acquire valid TLS certificates for the frp server's domain or IP address. You can use Let's Encrypt for free certificates or purchase them from a Certificate Authority.
    2. Configure TLS in frps.ini: In the [common] section of frps.ini, set tls_enable = true. Optionally, configure cert_file, key_file, and ca_file if you need to specify custom certificate paths or use client certificate verification.
    3. Configure TLS in frpc.ini: In the [common] section of frpc.ini, set tls_enable = true. No certificate configuration is typically needed on the client side unless using mTLS.
    4. Restart frp server and clients: Restart the frp server and all frp clients for TLS to be enabled for frp communication.

    • Threats Mitigated:

      • Man-in-the-Middle (MITM) Attacks on frp Traffic (High Severity): Without TLS, communication between frp clients and the server is in plain text, allowing attackers to intercept and potentially modify data transmitted through frp tunnels, including sensitive information and authentication tokens.
      • Eavesdropping on frp Traffic (High Severity): Plain text frp communication allows attackers to passively monitor network traffic and gain access to sensitive data transmitted through frp tunnels.

    • Impact:

      • MITM Attacks on frp Traffic: Significant reduction. TLS encryption makes it extremely difficult for attackers to intercept and modify frp communication.
      • Eavesdropping on frp Traffic: Significant reduction. TLS encryption prevents eavesdropping on frp traffic by encrypting all data in transit.

    • Currently Implemented: Fully implemented on the production frp server and all production clients for frp communication.

    • Missing Implementation: Ensure TLS is consistently enabled and configured correctly for frp communication across all environments (development, testing, staging, production). Regularly review TLS configuration for cipher strength and protocol versions used by frp.

Mitigation Strategy: Restrict Access using allow_users and deny_users in frp Proxy Definitions

  • Description:

    1. Define users in frpc.ini: In each frpc.ini file, within the [common] section, define a user parameter (e.g., user = client_user_name).
    2. Configure allow_users or deny_users in frps.ini proxy definitions: For each proxy definition in frps.ini (e.g., [ssh], [web]), add either allow_users = user1,user2 to explicitly allow access only to specified users, or deny_users = user3,user4 to deny access to specific users while allowing others to use that specific frp proxy.
    3. Restart frp server: Restart the frp server for the frp proxy access control changes to take effect.

    • Threats Mitigated:

      • Unauthorized Access to Specific frp Proxies (Medium Severity): Without user-based access control in frp proxy definitions, any authenticated frp client can potentially access any defined proxy, even if they are not authorized to access the underlying service exposed by that specific frp proxy.
      • Lateral Movement via frp Proxies (Medium Severity): If a compromised frp client gains access, restricting proxies based on users can limit the attacker's ability to move laterally to other internal services through unauthorized frp tunnels.

    • Impact:

      • Unauthorized Access to Specific frp Proxies: Moderate reduction. User-based access control in frp proxy definitions adds a layer of authorization, ensuring only intended clients can access specific services through specific frp proxies.
      • Lateral Movement via frp Proxies: Moderate reduction. Limits the scope of potential damage from a compromised frp client by restricting access to other services via frp.

    • Currently Implemented: Partially implemented. allow_users is used for some critical proxies in production, but not consistently applied across all frp proxies and environments.

    • Missing Implementation:

      • Implement allow_users or deny_users for all proxy definitions in production and staging environments to control access to services exposed via frp.
      • Develop a clear user management strategy for frp clients and proxies to effectively utilize allow_users and deny_users.

Mitigation Strategy: Limit Exposed Ports using allow_ports and deny_ports in frp Proxy Definitions

  • Description:

    1. Configure allow_ports or deny_ports in frps.ini proxy definitions: For each proxy definition in frps.ini, add allow_ports = 80,443,8080-8090 to allow only connections to specific ports or port ranges for that specific frp proxy, or deny_ports = 22,23 to block access to specific ports via that frp proxy.
    2. Restart frp server: Restart the frp server for the frp proxy port restriction changes to take effect.

    • Threats Mitigated:

      • Unnecessary Service Exposure via frp Proxies (Medium Severity): Without port restrictions in frp proxy definitions, proxies might inadvertently expose more ports than intended, increasing the attack surface through frp.
      • Port Scanning and Service Discovery via frp Proxies (Low Severity): Limiting exposed ports in frp proxy definitions makes it harder for attackers to discover and probe for vulnerable services through frp tunnels.

    • Impact:

      • Unnecessary Service Exposure via frp Proxies: Moderate reduction. Reduces the attack surface exposed via frp by limiting the ports accessible through frp proxies.
      • Port Scanning and Service Discovery via frp Proxies: Minor reduction. Makes reconnaissance slightly more difficult for attackers targeting services via frp.

    • Currently Implemented: Partially implemented. allow_ports is used for some proxies, but not consistently enforced, especially in development and testing environments.

    • Missing Implementation:

      • Implement allow_ports for all proxy definitions in production and staging environments, explicitly defining only the necessary ports for each frp proxy.
      • Regularly review and update allow_ports configurations to ensure they remain minimal and aligned with service requirements for each frp proxy.

Mitigation Strategy: Regularly Update frp to the Latest Stable Version

  • Description:

    1. Monitor frp releases: Subscribe to the frp project's GitHub releases or mailing lists to stay informed about new frp versions and security updates.
    2. Download the latest stable version: Obtain the latest stable release of frp from the official GitHub repository (https://github.com/fatedier/frp/releases).
    3. Replace existing frp binaries: Stop the running frp server and client processes. Replace the old frp server (frps) and client (frpc) binaries with the newly downloaded versions.
    4. Restart frp server and clients: Restart the frp server and all clients using the updated frp binaries.

    • Threats Mitigated:

      • Exploitation of Known frp Vulnerabilities (High Severity): Outdated frp software is vulnerable to publicly known security flaws in frp itself. Regularly updating frp patches these vulnerabilities, reducing the risk of exploitation of frp components.

    • Impact:

      • Exploitation of Known frp Vulnerabilities: Significant reduction. Keeps the frp installation protected against known security issues addressed in newer frp versions.

    • Currently Implemented: Partially implemented. Production frp server is updated periodically, but frp updates are not always applied promptly, and development/testing environments may lag behind in frp version.

    • Missing Implementation:

      • Establish a process for timely frp updates across all environments (development, testing, staging, production).
      • Automate the frp update process where possible to ensure consistent and rapid patching of frp vulnerabilities.
      • Implement a system to track frp versions in use and alert administrators when frp updates are available.