attack-surface.md

Attack Surface Analysis for fatedier/frp

Attack Surface: Exposure of frp Server Ports

• Description: frp server ports, such as bind_port, vhost_http_port, and vhost_https_port, are directly accessible from the public internet or untrusted networks.
• frp Contribution: frp server functionality necessitates listening on network ports. Default configurations can expose these ports without explicit security measures, making them directly reachable.
• Example: An attacker scans the internet and finds an open bind_port (default 7000) of an frp server. They attempt to connect as an unauthorized client to exploit vulnerabilities or use the server as an open proxy for malicious activities.
• Impact: Unauthorized access to the frp server, potential abuse as an open proxy, exposure of proxied internal services to the internet, and potential for further exploitation of internal network.
• Risk Severity: High
• Mitigation Strategies:
  • Restrict Access: Implement firewalls to limit access to the bind_port only to known and trusted frp client IP addresses or networks.
  • Network Segmentation: Deploy the frp server within a Demilitarized Zone (DMZ) or a dedicated network segment with strict inbound and outbound traffic rules.
  • Reverse Proxy/WAF for Web Ports: For vhost_http_port and vhost_https_port, consider placing a reverse proxy or Web Application Firewall (WAF) in front to add security layers and manage traffic before it reaches the frp server.

Attack Surface: Weak Authentication and Authorization

• Description: Insufficiently strong or improperly configured authentication and authorization mechanisms on the frp server allow unauthorized clients to connect and establish tunnels.
• frp Contribution: frp relies on a token for basic authentication. Weak or default tokens, or a lack of granular authorization controls within frp configuration, significantly weaken security.
• Example: An administrator uses the default token or a weak, easily guessable token in frps.toml. An attacker guesses or obtains this token and uses it to connect an unauthorized frp client, gaining the ability to create tunnels and potentially access sensitive internal resources.
• Impact: Unauthorized client connections, creation of malicious tunnels, potential data breaches by accessing proxied internal services, and unauthorized access to the internal network.
• Risk Severity: Critical
• Mitigation Strategies:
  • Strong Tokens: Generate and use strong, randomly generated, and unique token values in frps.toml. Avoid default or easily guessable tokens. Regularly rotate tokens.
  • Robust Authorization: Utilize frp's configuration options to implement granular authorization controls. Define precisely which clients are allowed to connect and what types of tunnels they are permitted to create.
  • Principle of Least Privilege: Configure client permissions and tunnel access based on the principle of least privilege, granting only the necessary access for legitimate purposes.

Attack Surface: Configuration Vulnerabilities and Misconfigurations

• Description: Insecure default configurations, overly permissive settings, or improper handling and exposure of frp configuration files (frps.toml, frpc.toml) lead to significant security weaknesses.
• frp Contribution: frp's security is heavily dependent on its configuration. Default configurations might not be hardened, and misconfigurations can easily introduce exploitable vulnerabilities.
• Example: Leaving the admin UI enabled and publicly accessible without strong authentication, configuring overly broad tunnel permissions allowing clients excessive access, or accidentally exposing frps.toml in a public repository revealing the server token.
• Impact: Exploitation of misconfigurations for unauthorized access, privilege escalation, denial of service, information disclosure (e.g., revealing tokens), and potential compromise of the frp server and connected systems.
• Risk Severity: High
• Mitigation Strategies:
  • Harden Configurations: Review and harden default configurations. Disable unnecessary features like the admin UI in production unless explicitly required and properly secured.
  • Secure Configuration Files: Restrict access to frps.toml and frpc.toml files. Store them securely with appropriate file permissions and consider encryption at rest. Avoid storing them in publicly accessible locations or version control systems without proper security measures.
  • Regular Configuration Audits: Periodically review frp configurations to identify and rectify any misconfigurations or deviations from security best practices. Use configuration management tools to enforce consistent and secure configurations.

Attack Surface: Denial of Service (DoS) Attacks on frp Server

• Description: Attackers attempt to overwhelm the frp server with excessive connection requests, tunnel creation attempts, or by exploiting protocol weaknesses, leading to service disruption and resource exhaustion.
• frp Contribution: As a central point for client connections and traffic routing, the frp server is a prime target for DoS attacks, potentially disrupting services reliant on frp.
• Example: An attacker launches a flood of connection requests to the frp server's bind_port, exhausting server resources (CPU, memory, network bandwidth) and preventing legitimate clients from connecting and establishing tunnels.
• Impact: Service unavailability for legitimate clients, disruption of application functionality relying on frp, and potential cascading failures in dependent systems due to loss of connectivity.
• Risk Severity: High
• Mitigation Strategies:
  • Rate Limiting and Connection Limits: Implement rate limiting and connection limits on the frp server to restrict the number of connections and requests from a single source within a given timeframe. Configure appropriate limits in frps.toml.
  • Resource Monitoring and Alerting: Monitor frp server resource utilization (CPU, memory, network) and set up alerts to detect unusual spikes that might indicate a DoS attack. Implement automated responses to mitigate DoS attempts.
  • Keep frp Updated: Regularly update the frp server software to the latest version to patch known vulnerabilities that could be exploited for DoS attacks.
  • Infrastructure Protection: Employ infrastructure-level DoS protection mechanisms, such as network firewalls and intrusion prevention systems, to filter malicious traffic before it reaches the frp server.

Attack Surface: Software Vulnerabilities in frp

• Description: Exploitable vulnerabilities exist in the frp server or client software code itself, which attackers can leverage to compromise the system.
• frp Contribution: Like any software, frp is susceptible to vulnerabilities. Using outdated versions or undiscovered zero-day vulnerabilities can expose the system to significant risk.
• Example: A publicly disclosed vulnerability (e.g., remote code execution, arbitrary file read) is discovered in a specific version of frp server. Attackers exploit this vulnerability on unpatched frp servers to gain control of the server, execute arbitrary code, and potentially compromise the underlying infrastructure.
• Impact: Complete compromise of the frp server or client, potentially leading to data breaches, system takeover, lateral movement within the network, and significant disruption of services.
• Risk Severity: Critical
• Mitigation Strategies:
  • Regular Updates: Establish a rigorous process for regularly updating frp server and client software to the latest stable versions. Subscribe to security advisories and vulnerability databases related to frp (e.g., GitHub repository watch, security mailing lists, vendor notifications).
  • Vulnerability Scanning and Penetration Testing: Incorporate vulnerability scanning tools into your security pipeline to proactively identify known vulnerabilities in deployed frp software. Conduct regular penetration testing to identify and address potential weaknesses.
  • Intrusion Detection and Prevention Systems (IDS/IPS): Implement IDS/IPS to detect and potentially block exploitation attempts targeting known frp vulnerabilities. Configure IDS/IPS rules to monitor for suspicious activity related to frp.

Attack Surface: Compromised frp Client Leading to Internal Network Access

• Description: If a machine running an frp client is compromised, attackers can leverage the established frp tunnels to gain unauthorized access to internal services and the internal network.
• frp Contribution: frp clients, by design, create tunnels into internal networks. A compromised client becomes a bridge for attackers to bypass perimeter security and access internal resources through these tunnels.
• Example: An attacker compromises a developer's workstation running an frp client through phishing or malware. They then utilize the compromised frp client and its existing tunnels to access internal databases, applications, or other sensitive services that were intended to be protected within the internal network.
• Impact: Unauthorized access to internal services, data exfiltration from internal networks, lateral movement within the internal network, and potential for further compromise of internal systems.
• Risk Severity: High
• Mitigation Strategies:
  • Harden Client Machines: Implement robust endpoint security measures on machines running frp clients, including operating system hardening, regular patching, antivirus software, Endpoint Detection and Response (EDR) solutions, and strong host-based firewalls.
  • Principle of Least Privilege on Clients: Run frp clients with minimal necessary privileges. Avoid running them as root or administrator if possible. Implement application whitelisting to restrict execution of unauthorized software.
  • Network Segmentation for Clients: Place frp client machines in a segmented network with restricted access to sensitive internal resources, limiting the potential impact of a client compromise. Implement micro-segmentation to further isolate client machines.
  • Regular Security Audits of Client Machines: Periodically audit the security posture of machines running frp clients to identify and remediate vulnerabilities. Enforce security policies and compliance on client endpoints.

Attack Surface: Man-in-the-Middle (MitM) Attacks on frp Communication

• Description: An attacker intercepts and potentially manipulates communication between the frp client and server if the communication channel is not properly secured with encryption and authentication.
• frp Contribution: If TLS encryption is not enabled for frp client-server communication, the traffic, including sensitive data and authentication tokens, is transmitted in plaintext and vulnerable to interception and manipulation.
• Example: An attacker positioned on the network path between an frp client and server intercepts the communication. Without TLS, they can read sensitive data being proxied through the tunnels, steal authentication tokens, or even inject malicious data into the communication stream to hijack tunnels or compromise proxied services.
• Impact: Data interception, data manipulation, potential hijacking of tunnels, compromise of proxied services, and potential for unauthorized access and further exploitation.
• Risk Severity: High
• Mitigation Strategies:
  • Enforce TLS Encryption: Always enable TLS encryption for communication between frp clients and servers by setting tls_enable = true in both frps.toml and frpc.toml. This is a critical security measure.
  • Proper TLS Configuration and Certificate Management: Ensure proper TLS certificate management and validation. Use valid, trusted certificates and configure clients to verify server certificates to prevent MitM attacks using forged certificates. Regularly renew and manage TLS certificates.

Attack Surface: Admin UI Exposure without Proper Authentication

• Description: If the optional admin UI of the frp server is enabled and exposed without strong authentication and authorization, it provides a direct interface for attackers to manage and control the frp server.
• frp Contribution: frp offers an optional admin UI for monitoring and management. If enabled and not adequately secured, it becomes a high-risk attack vector, granting administrative control to unauthorized users.
• Example: The admin UI is enabled in frps.toml and exposed on a public IP address or internal network without strong authentication (e.g., relying on default credentials or weak passwords). An attacker discovers the UI, attempts default credentials, brute-forces weak passwords, or exploits vulnerabilities in the UI to gain unauthorized access and reconfigure the frp server, potentially taking complete control.
• Impact: Unauthorized access to frp server management interface, leading to configuration changes, tunnel manipulation, server takeover, potential compromise of the entire frp infrastructure, and significant disruption of services.
• Risk Severity: High
• Mitigation Strategies:
  • Disable Admin UI in Production: The most effective mitigation is to disable the admin UI in production environments unless absolutely necessary for monitoring and management. This eliminates the attack surface entirely.
  • Strong Authentication for Admin UI (if enabled): If the admin UI is absolutely required, secure it with strong, non-default authentication credentials. Change default usernames and passwords immediately. Implement multi-factor authentication (MFA) for enhanced security.
  • Restrict Access to Admin UI: Limit access to the admin UI to trusted networks or IP addresses using firewall rules or access control lists. Consider using VPN access for administrators to reach the UI securely, avoiding direct exposure to public networks.

Attack Surface: Misconfigured Tunnels Leading to Unintended Exposure

• Description: Incorrectly configured tunnels on the frp client side can unintentionally expose internal services to the frp server and potentially beyond, if the server is exposed, leading to unintended access.
• frp Contribution: frp relies on user-defined tunnel configurations in frpc.toml. Misconfigurations due to errors, lack of understanding, or insufficient review can lead to accidental exposure of sensitive internal services.
• Example: A developer mistakenly configures a tunnel to expose a database port (e.g., port 5432) to the frp server, intending to expose only a web application. This unintentionally makes the database accessible through the frp server, potentially to unauthorized parties if the server is exposed or if authorization is not properly configured on the server side.
• Impact: Unintentional exposure of sensitive internal services (databases, internal applications, APIs), potentially leading to unauthorized access, data breaches, and other security incidents.
• Risk Severity: High
• Mitigation Strategies:
  • Rigorous Review of Tunnel Configurations: Implement a mandatory process for carefully reviewing and validating all frp client tunnel configurations before deployment. Ensure configurations are reviewed by security personnel or experienced administrators.
  • Configuration Management and Version Control: Manage frp client configurations using version control systems to track changes, facilitate audits, and enable rollback to previous secure configurations.
  • Approval Process for Tunnel Creation: Establish a formal approval process for creating new tunnels or modifying existing ones, involving security review and authorization from relevant stakeholders.
  • Least Privilege Tunnel Access: Configure tunnels to expose only the absolutely necessary services and ports. Avoid overly broad tunnel configurations that expose entire servers or network segments. Use specific bind addresses and ports in tunnel configurations to limit exposure.