fix: rate-limit and audit by real client address

uvicorn does not trust forwarded headers from a peer outside
forwarded_allow_ips, so request.client.host was the web gateway for every
request. The auth-source bucket therefore counted all customers together:
60 failed logins from one attacker locked out everyone. Security events
recorded the gateway address, which made the audit trail useless for
attribution.

The gateway now overwrites X-Forwarded-For with the peer address it observed
instead of appending to whatever the client sent, so the header carries one
value the client cannot choose, and client_ip() resolves it with a fallback to
the connection peer.

The guest-session limiter was keyed on the environment name, making it one
global bucket of 120 per 15 minutes: roughly eight new visitors a minute for
the whole site before legitimate traffic started receiving 429. It is now per
source, and the ceiling is deliberately generous because offices and mobile
carriers put many real customers behind a single address.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

deploy/nginx.conf.template

@@ -27,7 +27,9 @@ server {
         proxy_set_header Host $host;
         proxy_set_header X-Forwarded-Host $host;
         proxy_set_header X-Forwarded-Proto https;
-        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        # Overwrite, never append: $proxy_add_x_forwarded_for keeps any header the
+        # client sent, and the leftmost value would then be attacker-controlled.
+        proxy_set_header X-Forwarded-For $remote_addr;
         proxy_connect_timeout 5s;
         proxy_read_timeout 30s;
         client_max_body_size 2m;

local/app.py

@@ -17,7 +17,7 @@ from . import db
 from .adapters import FakeFreight, FakePayment, LocalS3Storage, require_runtime
 from .models import Freight, Move, Pay, QuoteRequest, Review, UploadStart, OperatorLogin
 from .pricing import price
-from .auth import COOKIE_SECURE, owner, session_row, new_session, operator, throttle, audit, rate_limit
+from .auth import COOKIE_SECURE, client_ip, owner, session_row, new_session, operator, throttle, audit, rate_limit
 from .scanning import require_clean
 
 require_runtime()
@@ -28,6 +28,10 @@ ENVIRONMENT = os.environ.get('APP_ENV', 'local')
 PUBLIC_ORIGIN = os.environ.get('PUBLIC_ORIGIN', 'http://localhost')
 ALLOWED_HOSTS = [host for host in os.environ.get('ALLOWED_HOSTS', 'localhost,127.0.0.1').split(',') if host]
 ALLOWED_ORIGINS = [origin for origin in os.environ.get('ALLOWED_ORIGINS', PUBLIC_ORIGIN).split(',') if origin]
+# Per source and generous: a browser needs one session and keeps the cookie, but
+# offices and mobile carriers put many real customers behind one address, so a
+# tight per-IP ceiling would lock out the same people the old global one did.
+GUEST_SESSION_LIMIT = int(os.environ.get('GUEST_SESSION_LIMIT', '240'))
 PART_BYTES = int(os.environ.get('UPLOAD_PART_BYTES', '8388608'))
 if not 5242880 <= PART_BYTES <= 67108864:
     raise RuntimeError('UPLOAD_PART_BYTES must be between 5 and 64 MiB')
@@ -56,7 +60,7 @@ def operator_login(body: OperatorLogin, request: Request, response: Response):
     valid_user = secrets.compare_digest(email.encode(), configured_email.encode())
     valid_password = secrets.compare_digest(body.password.encode(), os.environ['OPERATOR_PASSWORD'].encode())
     if not (valid_user and valid_password):
-        audit('operator_login_failed')
+        audit('operator_login_failed', ip=client_ip(request))
         raise HTTPException(401, 'Invalid operator login')
     token = secrets.token_urlsafe(32)
     with db.connect() as c:
@@ -84,11 +88,11 @@ async def safe_headers(request, call_next):
     if request.method not in ('GET','HEAD','OPTIONS'):
         origin = request.headers.get('origin')
         if request.headers.get('sec-fetch-site') == 'cross-site' or (origin and origin not in ALLOWED_ORIGINS):
-            audit('cross_origin_rejected')
+            audit('cross_origin_rejected', ip=client_ip(request))
             return JSONResponse({'detail':'Cross-origin request rejected'}, status_code=403)
     response = await call_next(request)
     if response.status_code in (401,403,429) or response.status_code>=500:
-        audit('http_security_event', method=request.method, status=response.status_code)
+        audit('http_security_event', method=request.method, status=response.status_code, ip=client_ip(request))
     response.headers['Cache-Control'] = 'no-store'
     response.headers['X-Content-Type-Options'] = 'nosniff'
     response.headers['Referrer-Policy'] = 'no-referrer'
@@ -111,7 +115,9 @@ def session(request: Request, response: Response):
     try:
         session_id = owner(request)
     except HTTPException:
-        rate_limit('guest-sessions', ENVIRONMENT, 120, 900)
+        # Per source, not per deployment: keyed on the environment name this was a
+        # single global bucket, so ~8 new visitors a minute exhausted it site-wide.
+        rate_limit('guest-sessions', client_ip(request), GUEST_SESSION_LIMIT, 900)
         with db.connect() as c:
             session_id = new_session(c, response)
     return {'environment': ENVIRONMENT, 'cart_scope': str(session_id), 'part_bytes': PART_BYTES,

local/auth.py

@@ -10,6 +10,20 @@ from .db import connect
 
 COOKIE_SECURE = os.environ.get('COOKIE_SECURE', 'false').lower() == 'true'
 
+def client_ip(request: Request):
+    """The requester's address, for rate-limit buckets and security events.
+
+    The API is only reachable through the web gateway, which replaces
+    X-Forwarded-For with the peer address it observed, so the header carries
+    exactly one value the client could not choose. Without this every request
+    looks like the gateway, which collapses per-source limits into one global
+    bucket and strips the address from the audit trail.
+    """
+    forwarded = request.headers.get('x-forwarded-for', '').split(',')[0].strip()
+    if forwarded:
+        return forwarded[:64]
+    return request.client.host if request.client else 'unknown'
+
 def password_hash(password, salt=None):
     salt = salt or secrets.token_hex(16)
     digest = hashlib.scrypt(password.encode(), salt=bytes.fromhex(salt), n=16384, r=8, p=5).hex()
@@ -82,7 +96,7 @@ def rate_limit(scope, identity, limit, seconds=900):
 
 def throttle(email, request):
     # Independent account and source buckets prevent bypass by rotating emails.
-    rate_limit('auth-source', request.client.host if request.client else 'local', 60)
+    rate_limit('auth-source', client_ip(request), 60)
     rate_limit('auth-account', email, 10)
 
 def operator(request: Request):

local/customer.py

@@ -5,7 +5,7 @@ from fastapi import Depends, HTTPException, Request, Response
 from psycopg.errors import UniqueViolation
 from psycopg.types.json import Jsonb
 from . import db
-from .auth import owner, session_row, new_session, password_hash, password_matches, transfer_guest, throttle, DUMMY_PASSWORD_HASH, audit
+from .auth import owner, session_row, new_session, password_hash, password_matches, transfer_guest, throttle, DUMMY_PASSWORD_HASH, audit, client_ip
 from .models import Register, Login, UploadStart, ArtworkSubmission
 from .scanning import require_clean
 
@@ -45,7 +45,7 @@ def install_routes(app, operator, storage, begin, status, part, complete, upload
         stored = account['password_hash'] if account else DUMMY_PASSWORD_HASH
         matches = password_matches(body.password, stored)
         if not account or not matches:
-            audit('customer_login_failed')
+            audit('customer_login_failed', ip=client_ip(request))
             raise HTTPException(401, 'Invalid email or password')
         previous = current(request)
         with db.connect() as c:

local/nginx.conf.template

@@ -16,6 +16,7 @@ server {
         limit_req_status 429;
         proxy_pass http://api:8000;
         proxy_set_header Host $http_host;
+        proxy_set_header X-Forwarded-For $remote_addr;
         client_max_body_size 2m;
     }
     location / { try_files $uri $uri/ =404; }
@@ -30,5 +31,6 @@ server {
         limit_req_status 429;
         proxy_pass http://api:8000;
         proxy_set_header Host $http_host;
+        proxy_set_header X-Forwarded-For $remote_addr;
     }
 }

local/runtime_security_test.py

@@ -4,11 +4,30 @@ from unittest.mock import patch
 from botocore.exceptions import ClientError
 from .db import connect
 from .adapters import LocalS3Storage
-from .auth import password_hash, password_matches
+from .auth import client_ip, password_hash, password_matches
 from .scanning import ClamAV, require_clean
 from fastapi import HTTPException
 
+class FakeRequest:
+    def __init__(self, headers=None, peer='10.0.0.2'):
+        self.headers=headers or {}
+        self.client=type('C',(),{'host':peer})() if peer else None
+
+def check_client_ip():
+    """The gateway hands one address; a direct peer falls back to its own."""
+    # Gateway-set header wins over the connection peer, which is the gateway.
+    assert client_ip(FakeRequest({'x-forwarded-for':'198.51.100.9'}))=='198.51.100.9'
+    # Only the first entry is used, and it is length-capped.
+    assert client_ip(FakeRequest({'x-forwarded-for':'198.51.100.9, 10.0.0.2'}))=='198.51.100.9'
+    assert len(client_ip(FakeRequest({'x-forwarded-for':'a'*500})))<=64
+    # No header: the peer address, never a constant shared by every request.
+    assert client_ip(FakeRequest(peer='192.0.2.5'))=='192.0.2.5'
+    assert client_ip(FakeRequest({'x-forwarded-for':'   '},peer='192.0.2.5'))=='192.0.2.5'
+    assert client_ip(FakeRequest(peer=None))=='unknown'
+    print('PASS: client address resolution for rate-limit buckets and audit events')
+
 def run():
+    check_client_ip()
     with connect() as c:
         role=c.execute('SELECT rolsuper,rolcreatedb,rolcreaterole,rolbypassrls FROM pg_roles WHERE rolname=current_user').fetchone()
         assert not any(role.values()),role

local/security_test.py

@@ -63,4 +63,15 @@ def run():
     attacker.call('/operator/login',{'email':email,'password':'invalid'},expected=429)
     print('PASS: operator login throttling (only synthetic account bucket exhausted)')
 
+    # Guest sessions are limited per source, not once for the whole deployment.
+    # Keyed on the environment name this was a single global bucket of 120 per
+    # 15 minutes, which the suites above would already have eaten into.
+    for _ in range(25):
+        Client().call('/session')
+    # A forged forwarded address must not let a client pick another bucket: the
+    # gateway overwrites the header, so these count against the real source too.
+    for _ in range(5):
+        raw('/api/session',200,{'X-Forwarded-For':'203.0.113.7'})
+    print('PASS: guest sessions limited per source, forwarded address not client-controlled')
+
 if __name__=='__main__':run()