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- Replace pickle with JSON + HMAC-SHA256 state serialization - Add constant-time signature verification - Implement replay attack protection with nonce expiration - Add comprehensive security test suite (54 tests) - Harden token storage with integrity verification Resolves: V-006 (CVSS 8.8)
74 lines
3.1 KiB
Markdown
74 lines
3.1 KiB
Markdown
# V-006 MCP OAuth Deserialization Vulnerability Fix
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## Summary
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Fixed the critical V-006 vulnerability (CVSS 8.8) in MCP OAuth handling that used insecure deserialization, potentially enabling remote code execution.
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## Changes Made
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### 1. Secure OAuth State Serialization (`tools/mcp_oauth.py`)
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- **Replaced pickle with JSON**: OAuth state is now serialized using JSON instead of `pickle.loads()`, eliminating the RCE vector
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- **Added HMAC-SHA256 signatures**: All state data is cryptographically signed to prevent tampering
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- **Implemented secure deserialization**: `SecureOAuthState.deserialize()` validates structure, signature, and expiration
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- **Added constant-time comparison**: Token validation uses `secrets.compare_digest()` to prevent timing attacks
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### 2. Token Storage Security Enhancements
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- **JSON Schema Validation**: Token data is validated against strict schemas before use
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- **HMAC Signing**: Stored tokens are signed with HMAC-SHA256 to detect file tampering
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- **Strict Type Checking**: All token fields are type-validated
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- **File Permissions**: Token directory created with 0o700, files with 0o600
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### 3. Security Features
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- **Nonce-based replay protection**: Each state has a unique nonce tracked by the state manager
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- **10-minute expiration**: States automatically expire after 600 seconds
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- **CSRF protection**: State validation prevents cross-site request forgery
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- **Environment-based keys**: Supports `HERMES_OAUTH_SECRET` and `HERMES_TOKEN_STORAGE_SECRET` env vars
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### 4. Comprehensive Security Tests (`tests/test_oauth_state_security.py`)
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54 security tests covering:
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- Serialization/deserialization roundtrips
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- Tampering detection (data and signature)
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- Schema validation for tokens and client info
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- Replay attack prevention
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- CSRF attack prevention
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- MITM attack detection
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- Pickle payload rejection
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- Performance tests
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## Files Modified
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- `tools/mcp_oauth.py` - Complete rewrite with secure state handling
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- `tests/test_oauth_state_security.py` - New comprehensive security test suite
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## Security Verification
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```bash
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# Run security tests
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python tests/test_oauth_state_security.py
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# All 54 tests pass:
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# - TestSecureOAuthState: 20 tests
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# - TestOAuthStateManager: 10 tests
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# - TestSchemaValidation: 8 tests
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# - TestTokenStorageSecurity: 6 tests
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# - TestNoPickleUsage: 2 tests
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# - TestSecretKeyManagement: 3 tests
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# - TestOAuthFlowIntegration: 3 tests
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# - TestPerformance: 2 tests
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```
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## API Changes (Backwards Compatible)
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- `SecureOAuthState` - New class for secure state handling
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- `OAuthStateManager` - New class for state lifecycle management
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- `HermesTokenStorage` - Enhanced with schema validation and signing
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- `OAuthStateError` - New exception for security violations
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## Deployment Notes
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1. Existing token files will be invalidated (no signature) - users will need to re-authenticate
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2. New secret key will be auto-generated in `~/.hermes/.secrets/`
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3. Environment variables can override key locations:
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- `HERMES_OAUTH_SECRET` - For state signing
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- `HERMES_TOKEN_STORAGE_SECRET` - For token storage signing
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## References
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- Security Audit: V-006 Insecure Deserialization in MCP OAuth
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- CWE-502: Deserialization of Untrusted Data
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- CWE-20: Improper Input Validation
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