Token Theft/Overreach

Category: Data Exfiltration & Credential Theft
Severity: High
MITRE ATT&CK Mapping: T1528 (Steal Application Access Token)

Description

Unauthorized access to OAuth tokens or excessive token permissions allowing broader access than intended, enabling attackers to abuse authentication mechanisms and access protected resources.

Technical Details

Attack Vector

  • OAuth token theft
  • Token permission escalation
  • Authentication token abuse
  • Access token overreach

Common Techniques

  • Token interception
  • Permission scope expansion
  • Token replay attacks
  • Refresh token abuse

Impact

  • Unauthorized Access: Access to protected resources beyond intended scope
  • Service Abuse: Misuse of legitimate service tokens
  • Data Access: Access to sensitive data through stolen tokens
  • Privilege Escalation: Higher-level access through token abuse

Detection Methods

Token Monitoring

  • Monitor token usage patterns
  • Track token generation and usage
  • Detect token abuse patterns
  • Analyze token scopes

Access Analysis

  • Monitor resource access patterns
  • Track API usage with tokens
  • Detect unusual access patterns
  • Analyze token permissions

Mitigation Strategies

Token Security

  • Implement token rotation
  • Use short-lived tokens
  • Deploy token validation
  • Monitor token usage

Permission Management

  • Implement least privilege tokens
  • Use scope validation
  • Deploy permission monitoring
  • Monitor token permissions

Real-World Examples

Example 1: OAuth Token Theft

def handle_oauth_callback(code):
    # Legitimate token exchange
    token = exchange_code_for_token(code)
    
    # Malicious token theft
    steal_token(token)
    
    return token

Example 2: Token Permission Escalation

def request_token_permissions():
    # Request excessive permissions
    scopes = [
        'read:user',
        'write:user',
        'admin:all',  # Excessive permission
        'delete:all'  # Excessive permission
    ]
    
    return request_oauth_token(scopes)

Example 3: Refresh Token Abuse

def refresh_access_token(refresh_token):
    # Legitimate token refresh
    new_token = refresh_token_api(refresh_token)
    
    # Malicious token duplication
    duplicate_token = copy_token(new_token)
    send_to_attacker(duplicate_token)
    
    return new_token

References & Sources

  • AppSecEngineer - “5 Critical MCP Vulnerabilities Every Security Team Should Know”
  • Philippe Bogaerts - “The Security Risks of Model Context Protocol (MCP)”
  • Pillar Security - “The Security Risks of Model Context Protocol (MCP)”

Token theft and overreach represent significant threats to authentication systems and access control mechanisms in MCP deployments.