Cross-Context Access

Category: Privilege & Access Control
Severity: High

Description

Unauthorized access across different security contexts, sessions, or user boundaries in MCP systems, enabling attackers to access resources from other users or contexts.

Technical Details

Attack Vector

Context isolation failures
Session boundary violations
User context switching
Security context bypass

Common Techniques

Context confusion attacks
Session hijacking
User impersonation
Security boundary violations

Impact

Data Access: Access to data from other users or contexts
Privacy Violation: Unauthorized access to user information
Context Compromise: Compromise of security contexts
System Integrity: Violation of system security boundaries

Detection Methods

Context Monitoring

Monitor context switching
Track cross-context access
Detect context violations
Analyze context integrity

Session Monitoring

Monitor session boundaries
Track session access
Detect session hijacking
Analyze session integrity

Mitigation Strategies

Context Isolation

Implement strong context isolation
Use secure session management
Deploy context monitoring
Regular context audits

Access Control

Implement context-aware access control
Use session-based permissions
Deploy access monitoring
Monitor context boundaries

Real-World Examples

Example 1: Session Context Mixing

# Vulnerable session management
class MCPSessionManager:
    def __init__(self):
        self.sessions = {}
        self.current_user = None
    
    def get_user_data(self, session_id):
        # Vulnerable: uses current_user instead of session user
        if session_id in self.sessions:
            return self.get_data_for_user(self.current_user)
        
        # Attacker accesses another user's data
        # session_id = "victim_session"
        # current_user = "attacker"

Example 2: Context Boundary Violation

# Vulnerable context isolation
class MCPContextManager:
    def __init__(self):
        self.contexts = {}
        self.shared_resources = {}
    
    def access_resource(self, context_id, resource_id):
        # Insufficient context validation
        if context_id in self.contexts:
            # Should validate resource belongs to context
            return self.shared_resources.get(resource_id)
        
        # Attacker accesses resources from other contexts
        # context_id = "user_context"
        # resource_id = "admin_resource"

Example 3: User Context Switching

# Vulnerable user context switching
class MCPUserContext:
    def __init__(self):
        self.current_user = None
        self.user_data = {}
    
    def switch_user(self, new_user):
        # Insufficient validation
        self.current_user = new_user
    
    def get_user_files(self):
        # Returns files for current user
        return self.user_data.get(self.current_user, [])
    
    def process_request(self, request):
        # Vulnerable: user switching without validation
        if request.get('switch_user'):
            self.switch_user(request['switch_user'])
        
        # Attacker switches to another user context
        # request = {"switch_user": "admin", "action": "get_files"}

References & Sources

Equixly - “MCP Servers: The New Security Nightmare”
Red Hat - “Model Context Protocol (MCP): Understanding security risks and controls”

Cross-context access vulnerabilities can lead to serious privacy violations and unauthorized access to sensitive user data and system resources.