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Server listening on interfaces accessible beyond the local machine when not intended.

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How to resolve

  • Bind to localhost: Configure the MCP server to bind only to localhost (127.0.0.1 or ::1 for IPv6) if it is intended for local-only access. Review the server’s binding configuration in its startup parameters or configuration files and change from 0.0.0.0 or specific interface addresses to 127.0.0.1.
  • Use strong authentication: If the server must be accessible over the network for legitimate reasons, implement additional security controls including strong authentication, TLS encryption, network firewalls, and IP-based access restrictions.
  • Implement network-level restrictions: Use network segmentation to isolate MCP servers on trusted internal networks. Deploy a reverse proxy or API gateway to mediate external access with additional security controls.
  • Audit: Regularly audit listening ports using tools like netstat to verify binding configurations match security requirements. Document the intended access scope for each MCP server deployment.

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Risk

Governance/Compliance Exposed port vulnerabilities violate multiple security standards:
  • NIST Cybersecurity Framework 2.0 (PR.IR-01): Violates network integrity protection requirements by exposing services to unauthorized network segments.
  • OWASP Top10 A02:2025 Security Misconfiguration: Applications are vulnerable when unnecessary features such as ports are enabled.
Security When MCP servers are unintentionally exposed to broader networks, they become accessible to unauthorized parties who can attempt authentication bypass, exploit vulnerabilities, or launch denial-of-service attacks. This exposure is particularly dangerous for servers that lack robust authentication mechanisms or contain security vulnerabilities, as attackers anywhere on the accessible network can attempt exploitation. Exposed ports also enable reconnaissance activities where attackers can enumerate available tools, probe for weaknesses, and plan targeted attacks. For MCP servers intended only for local LLM applications, network exposure provides no legitimate benefit while creating significant unnecessary risk.

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Explanation

This issue is raised when an MCP server is configured to listen on network interfaces that are accessible beyond the local machine when this broader exposure is not intended. Servers bound to 0.0.0.0 or public IP addresses accept connections from any network location, whereas servers intended for local use only should bind to 127.0.0.1 (localhost). Unnecessary network exposure increases the attack surface and risk of unauthorized access.

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Specifications

Trigger
  • MCP server scan detects that the server is bound to 0.0.0.0, a public IP address, or network interfaces accessible from outside the local machine when only local access is appropriate.
Severity
  • MEDIUM
Applies to: MCP Server