sfi issue fix

Author: Ravikirana-Microsoft

src/frontend/frontend_server.py

@@ -3,7 +3,8 @@
 
 import uvicorn
 from dotenv import load_dotenv
-from fastapi import FastAPI
+from pathlib import Path
+from fastapi import FastAPI, HTTPException, Request
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.responses import FileResponse, HTMLResponse
 from fastapi.staticfiles import StaticFiles
@@ -24,12 +25,30 @@
 BUILD_DIR = os.path.join(os.path.dirname(__file__), "build")
 INDEX_HTML = os.path.join(BUILD_DIR, "index.html")
 
+# Resolved build directory path (used to prevent path traversal)
+BUILD_DIR_PATH = Path(BUILD_DIR).resolve()
+
+# Security: block serving of certain sensitive files by extension/name
+FORBIDDEN_EXTENSIONS = {'.env', '.py', '.pem', '.key', '.db', '.sqlite', '.toml', '.ini'}
+FORBIDDEN_FILENAMES = {'Dockerfile', '.env', '.secrets', '.gitignore'}
+
 # Serve static files from build directory
 app.mount(
     "/assets", StaticFiles(directory=os.path.join(BUILD_DIR, "assets")), name="assets"
 )
 
 
+@app.middleware("http")
+async def add_security_headers(request: Request, call_next):
+    resp = await call_next(request)
+    # Basic security headers; applications should extend CSP per app needs
+    resp.headers.setdefault("X-Content-Type-Options", "nosniff")
+    resp.headers.setdefault("X-Frame-Options", "DENY")
+    resp.headers.setdefault("Referrer-Policy", "no-referrer")
+    resp.headers.setdefault("Permissions-Policy", "geolocation=(), microphone=()")
+    return resp
+
+
 @app.get("/")
 async def serve_index():
     return FileResponse(INDEX_HTML)
@@ -50,12 +69,57 @@ async def get_config():
 
 @app.get("/{full_path:path}")
 async def serve_app(full_path: str):
-    # First check if file exists in build directory
-    file_path = os.path.join(BUILD_DIR, full_path)
-    if os.path.exists(file_path):
-        return FileResponse(file_path)
-    # Otherwise serve index.html for client-side routing
-    return FileResponse(INDEX_HTML)
+    """
+    Safely serve static files from the build directory or return the SPA index.html.
+
+    Protections:
+    - Prevent directory traversal by resolving candidate paths and ensuring they are inside BUILD_DIR.
+    - Block dotfiles and sensitive extensions/names.
+    - Return 404 on suspicious access instead of leaking details.
+    """
+    try:
+        candidate = (BUILD_DIR_PATH / full_path).resolve()
+
+        # Ensure resolved path is within BUILD_DIR
+        if not str(candidate).startswith(str(BUILD_DIR_PATH)):
+            raise HTTPException(status_code=404)
+
+        # Compute relative parts and block dotfiles anywhere in path
+        try:
+            rel_parts = candidate.relative_to(BUILD_DIR_PATH).parts
+        except Exception:
+            raise HTTPException(status_code=404)
+
+        if any(part.startswith('.') for part in rel_parts):
+            raise HTTPException(status_code=404)
+
+        if candidate.name in FORBIDDEN_FILENAMES:
+            raise HTTPException(status_code=404)
+
+        # If it's a regular file and allowed extension, serve it
+        if candidate.is_file():
+            if candidate.suffix.lower() in FORBIDDEN_EXTENSIONS:
+                raise HTTPException(status_code=404)
+
+            headers = {
+                "X-Content-Type-Options": "nosniff",
+                "X-Frame-Options": "DENY",
+                "Referrer-Policy": "no-referrer",
+            }
+            return FileResponse(str(candidate), headers=headers)
+
+        # Not a file -> fall back to SPA entrypoint
+        return FileResponse(INDEX_HTML, headers={
+            "X-Content-Type-Options": "nosniff",
+            "X-Frame-Options": "DENY",
+            "Referrer-Policy": "no-referrer",
+        })
+
+    except HTTPException:
+        raise
+    except Exception:
+        # Hide internal errors and respond with 404 to avoid information leakage
+        raise HTTPException(status_code=404)
 
 
 if __name__ == "__main__":