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MCP_SECURITY.md

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+# MCP Read-Only Security Guide
+
+## Current Security Measures
+
+The `mssql-mcp-readonly.js` file implements multiple layers of read-only enforcement:
+
+### 1. Query Validation (Application Layer)
+- ✅ Only SELECT queries allowed
+- ✅ Blocks INSERT, UPDATE, DELETE, DROP, CREATE, ALTER, TRUNCATE
+- ✅ Blocks EXEC/EXECUTE (prevents stored procedure execution)
+- ✅ Blocks SP_/XP_ (prevents system stored procedures)
+- ✅ Blocks MERGE, GRANT, REVOKE, DENY
+- ✅ Prevents query chaining with semicolons
+
+### 2. Recommended: Database User Permissions (Database Layer)
+
+For **maximum security**, create a read-only database user:
+
+```sql
+-- Create a read-only user
+CREATE LOGIN mcp_readonly WITH PASSWORD = 'YourSecurePassword123!';
+USE Infra;
+CREATE USER mcp_readonly FOR LOGIN mcp_readonly;
+
+-- Grant only SELECT permission
+GRANT SELECT ON SCHEMA::dbo TO mcp_readonly;
+
+-- Or grant SELECT on specific tables only:
+GRANT SELECT ON dbo.SDS_Teile TO mcp_readonly;
+GRANT SELECT ON dbo.SDS_Teile_CA TO mcp_readonly;
+GRANT SELECT ON dbo.SDS_Teile_CS TO mcp_readonly;
+GRANT SELECT ON dbo.SDS_Teile_LC TO mcp_readonly;
+GRANT SELECT ON dbo.SDS_Teile_ME TO mcp_readonly;
+GRANT SELECT ON dbo.SDS_Teile_MK TO mcp_readonly;
+GRANT SELECT ON dbo.SDS_Teile_MS TO mcp_readonly;
+GRANT SELECT ON dbo.SDS_Teile_WT TO mcp_readonly;
+GRANT SELECT ON dbo.SDS_Teile_EL TO mcp_readonly;
+
+-- Explicitly deny write permissions (extra safety)
+DENY INSERT, UPDATE, DELETE, ALTER ON SCHEMA::dbo TO mcp_readonly;
+```
+
+### 3. Update MCP Configuration
+
+After creating the read-only user, update `~/.cursor/mcp.json`:
+
+```json
+{
+  "mcpServers": {
+    "mssql-mcp-readonly": {
+      "command": "node ",
+      "args": ["/home/sdsadmin/infraviewer/mssql-mcp-readonly.js"],
+      "env": {
+        "MSSQL_SERVER": "192.168.120.88",
+        "MSSQL_PORT": "1433",
+        "MSSQL_USER": "mcp_readonly",
+        "MSSQL_PASSWORD": "YourSecurePassword123!",
+        "MSSQL_DATABASE": "Infra",
+        "MSSQL_ENCRYPT": "true",
+        "MSSQL_TRUST_SERVER_CERTIFICATE": "true"
+      }
+    }
+  }
+}
+```
+
+## Security Layers
+
+| Layer | Protection | Bypassed if... |
+|-------|-----------|----------------|
+| **Application Validation** | Keyword blocking | Code has bugs |
+| **Database Permissions** | SQL Server enforced | Wrong credentials used |
+| **Both Combined** | Double protection | Nearly impossible ✅ |
+
+## Testing Read-Only Access
+
+### Test 1: Valid SELECT (should work)
+```sql
+SELECT TOP 10 * FROM SDS_Teile
+```
+
+### Test 2: Invalid INSERT (should fail)
+```sql
+INSERT INTO SDS_Teile (Teil) VALUES ('TEST')
+```
+**Expected:** Error: "Forbidden keyword detected: INSERT"
+
+### Test 3: Query Chaining (should fail)
+```sql
+SELECT 1; DROP TABLE SDS_Teile
+```
+**Expected:** Error: "Multiple statements not allowed"
+
+### Test 4: Stored Procedure (should fail)
+```sql
+EXEC sp_helpdb
+```
+**Expected:** Error: "Forbidden keyword detected: EXEC"
+
+## Current vs Recommended Setup
+
+### Current Setup (Application Layer Only)
+```
+[AI] → [mssql-mcp-readonly.js] → [SQL Server]
+         ↑ Validates queries          ↑ Full permissions
+```
+**Risk:** If validation code has a bug, data could be modified
+
+### Recommended Setup (Defense in Depth)
+```
+[AI] → [mssql-mcp-readonly.js] → [SQL Server with read-only user]
+         ↑ Validates queries          ↑ SELECT-only permissions
+```
+**Benefit:** Even if validation fails, SQL Server will block write operations
+
+## Monitoring
+
+Check MCP server logs for blocked attempts:
+```bash
+# If running as systemd service
+journalctl -u mcp-readonly -f
+
+# If running manually
+tail -f /var/log/mcp-readonly.log
+```
+
+## Best Practices
+
+1. ✅ Use dedicated read-only database user
+2. ✅ Keep validation keywords up to date
+3. ✅ Monitor for failed query attempts
+4. ✅ Regularly audit database permissions
+5. ✅ Use strong passwords for database users
+6. ✅ Enable SQL Server audit logging
+7. ✅ Limit network access to database server
+8. ✅ Keep mssql package updated (`npm update mssql`)
+
+## Additional Hardening
+
+### 1. Add Query Size Limits
+Prevent resource exhaustion:
+```javascript
+function validateQuery(query) {
+  if (query.length > 10000) {
+    throw new Error("Query too long!");
+  }
+  // ... rest of validation
+}
+```
+
+### 2. Add Rate Limiting
+Prevent abuse:
+```javascript
+const rateLimit = require('express-rate-limit');
+// Limit to 100 queries per minute
+```
+
+### 3. Add Query Logging
+Track all queries:
+```javascript
+console.log(`[${new Date().toISOString()}] Query: ${query.substring(0, 100)}...`);
+```
+
+