Add security headers, external CSS, HTML escaping

- Middleware sets CSP (default-src 'none'; style-src 'self'), HSTS,
  X-Content-Type-Options, X-Frame-Options, Referrer-Policy,
  Permissions-Policy on every response
- Inline <style> moved to /styles.css so CSP needs no unsafe-inline
- /favicon.ico returns a 1x1 GIF (kills 404 noise)
- Escape LLM jokes, article title, and URL before HTML rendering (XSS fix)

app/main.py

@@ -1,3 +1,4 @@
+import html
 import logging
 from contextlib import asynccontextmanager
 from datetime import date
@@ -5,14 +6,14 @@ from datetime import date
 from apscheduler.schedulers.asyncio import AsyncIOScheduler
 from apscheduler.triggers.cron import CronTrigger
 from apscheduler.triggers.interval import IntervalTrigger
-from fastapi import FastAPI
-from fastapi.responses import HTMLResponse, JSONResponse
+from fastapi import FastAPI, Request
+from fastapi.responses import HTMLResponse, JSONResponse, Response
 from zoneinfo import ZoneInfo
 
 from . import db
 from .config import settings
 from .generator import generation_exhausted, run_generation, today_local
-from .templates import PAGE_TEMPLATE
+from .templates import CSS, PAGE_TEMPLATE
 
 logging.basicConfig(
     level=logging.INFO,
@@ -64,6 +65,42 @@ async def lifespan(app: FastAPI):
 
 app = FastAPI(title="Wiki Jokes", lifespan=lifespan)
 
+SECURITY_HEADERS = {
+    "Content-Security-Policy": (
+        "default-src 'none'; style-src 'self'; img-src 'self' data:; "
+        "base-uri 'none'; form-action 'none'; frame-ancestors 'none'"
+    ),
+    "X-Content-Type-Options": "nosniff",
+    "X-Frame-Options": "DENY",
+    "Referrer-Policy": "no-referrer",
+    "Strict-Transport-Security": "max-age=31536000; includeSubDomains",
+    "Permissions-Policy": "camera=(), microphone=(), geolocation=()",
+}
+
+
+@app.middleware("http")
+async def security_headers(request: Request, call_next):
+    response = await call_next(request)
+    for key, value in SECURITY_HEADERS.items():
+        response.headers[key] = value
+    return response
+
+
+@app.get("/styles.css")
+def styles():
+    return Response(content=CSS, media_type="text/css")
+
+
+@app.get("/favicon.ico")
+def favicon():
+    # Tiny 1x1 transparent GIF; stops 404 noise and scanner probing.
+    import base64
+
+    return Response(
+        content=base64.b64decode("R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7"),
+        media_type="image/gif",
+    )
+
 
 @app.get("/", response_class=HTMLResponse)
 def index():
@@ -80,7 +117,7 @@ def index():
             status_code=503,
         )
     items = "\n".join(
-        f'      <li class="joke">{j}</li>' for j in batch["jokes"]
+        f'      <li class="joke">{html.escape(j)}</li>' for j in batch["jokes"]
     )
     stale_note = (
         '<p class="stale">⚠️ Today\'s jokes are still being prepared — '
@@ -92,8 +129,8 @@ def index():
         day=batch["day"],
         stale_note=stale_note,
         jokes=items,
-        article_title=batch["article_title"],
-        article_url=batch["article_url"],
+        article_title=html.escape(batch["article_title"]),
+        article_url=html.escape(batch["article_url"], quote=True),
     )
 
 

app/templates.py

@@ -1,40 +1,42 @@
+CSS = """
+:root { color-scheme: light dark; }
+body {
+  font-family: Georgia, 'Times New Roman', serif;
+  max-width: 720px; margin: 0 auto; padding: 2rem 1rem;
+  background: #fdfcf8; color: #222;
+}
+@media (prefers-color-scheme: dark) {
+  body { background: #1a1a1e; color: #e8e6e1; }
+  a { color: #8ab4f8; }
+  .joke { background: #26262c; color: #eceae4; border-color: #3a3a42; }
+  header h1 { color: #f0ede6; }
+}
+header h1 { font-size: 2rem; margin-bottom: .25rem; }
+.date { color: #777; margin-top: 0; }
+.stale {
+  background: #fff3cd; color: #665100; padding: .5rem .75rem;
+  border-radius: 6px; font-size: .9rem;
+}
+@media (prefers-color-scheme: dark) {
+  .stale { background: #4a3c0a; color: #ffd970; }
+}
+ul.jokes { list-style: none; padding: 0; }
+li.joke {
+  background: #fff; color: #222; border: 1px solid #e2ddd2; border-radius: 10px;
+  padding: 1rem 1.25rem; margin: .9rem 0; font-size: 1.15rem;
+  line-height: 1.5; box-shadow: 0 1px 3px rgba(0,0,0,.06);
+}
+li.joke::before { content: "\\1F604  "; }
+footer { margin-top: 2rem; font-size: .9rem; color: #888; }
+"""
+
 PAGE_TEMPLATE = """<!DOCTYPE html>
 <html lang="en">
 <head>
 <meta charset="utf-8">
 <meta name="viewport" content="width=device-width, initial-scale=1">
 <title>Wiki Jokes — {day}</title>
-<style>
-  :root {{ color-scheme: light dark; }}
-  body {{
-    font-family: Georgia, 'Times New Roman', serif;
-    max-width: 720px; margin: 0 auto; padding: 2rem 1rem;
-    background: #fdfcf8; color: #222;
-  }}
-  @media (prefers-color-scheme: dark) {{
-    body {{ background: #1a1a1e; color: #e8e6e1; }}
-    a {{ color: #8ab4f8; }}
-    .joke {{ background: #26262c; color: #eceae4; border-color: #3a3a42; }}
-    header h1 {{ color: #f0ede6; }}
-  }}
-  header h1 {{ font-size: 2rem; margin-bottom: .25rem; }}
-  .date {{ color: #777; margin-top: 0; }}
-  .stale {{
-    background: #fff3cd; color: #665100; padding: .5rem .75rem;
-    border-radius: 6px; font-size: .9rem;
-  }}
-  @media (prefers-color-scheme: dark) {{
-    .stale {{ background: #4a3c0a; color: #ffd970; }}
-  }}
-  ul.jokes {{ list-style: none; padding: 0; }}
-  li.joke {{
-    background: #fff; color: #222; border: 1px solid #e2ddd2; border-radius: 10px;
-    padding: 1rem 1.25rem; margin: .9rem 0; font-size: 1.15rem;
-    line-height: 1.5; box-shadow: 0 1px 3px rgba(0,0,0,.06);
-  }}
-  li.joke::before {{ content: "😄 "; }}
-  footer {{ margin-top: 2rem; font-size: .9rem; color: #888; }}
-</style>
+<link rel="stylesheet" href="/styles.css">
 </head>
 <body>
   <header>
@@ -47,7 +49,7 @@ PAGE_TEMPLATE = """<!DOCTYPE html>
   </ul>
   <footer>
     Inspired by today's Wikipedia featured article:
-    <a href="{article_url}" rel="noopener">{article_title}</a>
+    <a href="{article_url}" rel="noopener noreferrer">{article_title}</a>
   </footer>
 </body>
 </html>