feat(security): add CORS and TrustedHost middleware

- Adds `CORSMiddleware` and `TrustedHostMiddleware` to FastAPI app.
- Configures `ALLOWED_ORIGINS` and `ALLOWED_HOSTS` via environment variables.
- Defaults to `*` for both, ensuring backward compatibility.
- Adds test to verify middleware configuration.
- Updates Sentinel journal with security finding.

Co-authored-by: lgcorzo <46710567+lgcorzo@users.noreply.github.com>

Author: google-labs-jules[bot]

.jules/sentinel.md

@@ -12,3 +12,8 @@
 **Vulnerability:** The application was catching exceptions in logic callbacks and Kafka consumers, then assigning the raw exception string to a JSON `error` field in the successful response object. This leaked internal details even when the HTTP status code was 200 OK or when processing asynchronously via Kafka.
 **Learning:** Checking for HTTP 500 handlers is not enough. Review application-level error handling where business logic manually constructs error objects.
 **Prevention:** Ensure that any `result["error"]` or similar fields populated in catch blocks use generic messages, while the real exception is logged server-side.
+
+## 2026-02-10 - Missing Security Middleware
+**Vulnerability:** The FastAPI application lacked `CORSMiddleware` and `TrustedHostMiddleware`, leaving it vulnerable to Cross-Origin attacks and Host Header attacks.
+**Learning:** Default FastAPI applications do not include security headers or CORS protection by default.
+**Prevention:** Always configure `CORSMiddleware` and `TrustedHostMiddleware` with strict, environment-configurable allowlists (e.g., `ALLOWED_ORIGINS`, `ALLOWED_HOSTS`).

src/regression_model_template/controller/kafka_app.py

@@ -12,6 +12,8 @@
 import uvicorn
 import pandas as pd
 from fastapi import FastAPI, HTTPException
+from fastapi.middleware.cors import CORSMiddleware
+from fastapi.middleware.trustedhost import TrustedHostMiddleware
 from pydantic import BaseModel
 
 from confluent_kafka import Producer, Consumer, KafkaError, Message
@@ -29,6 +31,9 @@
 DEFAULT_OUTPUT_TOPIC = os.getenv("DEFAULT_OUTPUT_TOPIC", "output_topic")
 DEFAULT_FASTAPI_HOST = os.getenv("DEFAULT_FASTAPI_HOST", "127.0.0.1")
 DEFAULT_FASTAPI_PORT = int(os.getenv("DEFAULT_FASTAPI_PORT", 8100))
+# Security: Configure allowed origins and hosts via environment variables
+ALLOWED_ORIGINS = os.getenv("ALLOWED_ORIGINS", "*").split(",")
+ALLOWED_HOSTS = os.getenv("ALLOWED_HOSTS", "*").split(",")
 LOGGING_FORMAT = "%(asctime)s - %(levelname)s - %(message)s"
 
 
@@ -43,6 +48,20 @@
     version="1.0.0",
 )
 
+# Security Middleware
+app.add_middleware(
+    TrustedHostMiddleware,
+    allowed_hosts=ALLOWED_HOSTS,
+)
+
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=ALLOWED_ORIGINS,
+    allow_credentials=True,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
 
 # Data Models
 class PredictionRequest(BaseModel):

tests/controller/test_kafka_app_middleware.py

@@ -0,0 +1,26 @@
+from fastapi.middleware.cors import CORSMiddleware
+from fastapi.middleware.trustedhost import TrustedHostMiddleware
+from regression_model_template.controller.kafka_app import app, ALLOWED_ORIGINS, ALLOWED_HOSTS
+
+
+def test_security_middleware_present():
+    """Test that security middleware is added to the FastAPI app."""
+    middleware_cls = [m.cls for m in app.user_middleware]
+
+    assert CORSMiddleware in middleware_cls, "CORSMiddleware should be present"
+    assert TrustedHostMiddleware in middleware_cls, "TrustedHostMiddleware should be present"
+
+
+def test_security_middleware_configuration():
+    """Test that security middleware is configured correctly."""
+
+    # Check CORSMiddleware config
+    cors_middleware = next(m for m in app.user_middleware if m.cls == CORSMiddleware)
+    # Starlette Middleware stores args in kwargs
+    assert cors_middleware.kwargs["allow_origins"] == ALLOWED_ORIGINS
+    assert cors_middleware.kwargs["allow_origins"] == ["*"]  # Default
+
+    # Check TrustedHostMiddleware config
+    trusted_host_middleware = next(m for m in app.user_middleware if m.cls == TrustedHostMiddleware)
+    assert trusted_host_middleware.kwargs["allowed_hosts"] == ALLOWED_HOSTS
+    assert trusted_host_middleware.kwargs["allowed_hosts"] == ["*"]  # Default