Auth Bypass & Rogue Server Registration

Category: Authentication & Authorization
Severity: High
MITRE ATT&CK Mapping: T1190 (Exploit Public-Facing Application)

Description

Unauthorized server registration and unverified API usage, enabling attackers to register malicious MCP servers or bypass authentication requirements for server registration.

Technical Details

Attack Vector

  • Unverified server registration
  • Authentication bypass in registration
  • Rogue server deployment
  • API authentication bypass

Common Techniques

  • Registration endpoint exploitation
  • Authentication bypass
  • Identity spoofing
  • Server impersonation

Impact

  • Rogue Server Deployment: Malicious servers registered in MCP ecosystem
  • Service Impersonation: Legitimate services impersonated by malicious servers
  • Trust Exploitation: Abuse of server trust mechanisms
  • System Compromise: Access through unauthorized servers

Detection Methods

Registration Monitoring

  • Monitor server registration attempts
  • Track registration patterns
  • Detect unauthorized registrations
  • Analyze registration data

Server Validation

  • Verify server authenticity
  • Monitor server behavior
  • Detect rogue servers
  • Analyze server identity

Mitigation Strategies

Registration Security

  • Implement server authentication
  • Use registration validation
  • Deploy server verification
  • Monitor registration attempts

Server Trust Management

  • Implement server trust mechanisms
  • Use server certificates
  • Deploy server validation
  • Monitor server behavior

Real-World Examples

Example 1: Unverified Registration

def register_server(server_info):
    # No verification of server identity
    server_id = generate_server_id()
    save_server(server_id, server_info)
    
    # Should include: verify_server_authenticity()
    return {"server_id": server_id, "status": "registered"}

Example 2: Authentication Bypass

def register_mcp_server(server_data, auth_token=None):
    # Authentication bypass for "local" servers
    if server_data.get("type") == "local":
        return register_server_direct(server_data)
    
    # Normal authentication for remote servers
    if not validate_auth_token(auth_token):
        return {"error": "Unauthorized"}
    
    return register_server_direct(server_data)

Example 3: Identity Spoofing

def validate_server_identity(server_name, server_cert):
    # Weak identity validation
    if server_name in trusted_servers:
        return True
    
    # Attack: server_name = "google-drive-connector" (similar to "google_drive_connector")
    # Bypasses validation through name similarity

References & Sources

  • Structured MCP Threats - Comprehensive threat landscape analysis

Auth bypass and rogue server registration attacks compromise the integrity of the MCP server ecosystem by enabling unauthorized server deployment.