fix: restrict Web Push endpoint egress (Closes #653)

README.md

@@ -199,6 +199,9 @@ export STACKCHAIN_TRUSTED_PROXY_CIDRS='127.0.0.0/8'
 # three individual alerts followed by one private digest that opens Updates. A later
 # comment on an already-delivered thread triggers a fresh alert when Gitea advances
 # that thread's updated_at revision; unchanged and older snapshots remain silent.
+# Browser push services must resolve exclusively to public IP addresses. Stackchain
+# validates endpoints at enrollment and again before delivery, rejects redirects,
+# and removes legacy subscriptions that resolve to private or reserved networks.
 export STACKCHAIN_VAPID_PUBLIC_KEY='<url-safe-public-key>'
 export STACKCHAIN_VAPID_PRIVATE_KEY='<private-key-from-secret-manager>'
 export STACKCHAIN_VAPID_SUBJECT='mailto:ops@example.com'

src/main.py

@@ -48,6 +48,7 @@ from src.live_snapshot_store import (
 from src.models import Issue, Milestone, PullRequest, Repo, User
 from src.passkey_store import PasskeyStore
 from src.push_notifications import PushConfiguration, dispatch_unread_updates
+from src.push_endpoint_policy import UnsafePushEndpoint, validate_public_push_endpoint
 from src.push_subscription_store import PushSubscriptionStore
 from src.request_boundary import RequestBodyLimitMiddleware, request_body_limit
 from src.security_event_store import SecurityEventStore, SecurityEventStoreError
@@ -1808,6 +1809,10 @@ async def push_status(request: Request):
 async def subscribe_push(payload: PushSubscriptionPayload, request: Request):
     if not _push_configuration().enabled:
         raise HTTPException(status_code=503, detail="Push notifications are not configured")
+    try:
+        await validate_public_push_endpoint(payload.endpoint)
+    except UnsafePushEndpoint as error:
+        raise HTTPException(status_code=422, detail=str(error)) from error
     device_id = await dashboard_auth.session_management_id(
         request.state.dashboard_session
     )

src/push_endpoint_policy.py

@@ -0,0 +1,62 @@
+import asyncio
+import ipaddress
+import socket
+from collections.abc import Awaitable, Callable
+from urllib.parse import urlsplit
+
+
+class UnsafePushEndpoint(ValueError):
+    """Raised when a Web Push endpoint could reach a non-public service."""
+
+
+Resolver = Callable[[str, int], Awaitable[list[str]]]
+
+
+async def _resolve(host: str, port: int) -> list[str]:
+    loop = asyncio.get_running_loop()
+    records = await loop.getaddrinfo(
+        host,
+        port,
+        family=socket.AF_UNSPEC,
+        type=socket.SOCK_STREAM,
+    )
+    return sorted({record[4][0] for record in records})
+
+
+async def validate_public_push_endpoint(
+    endpoint: str,
+    *,
+    resolver: Resolver = _resolve,
+    timeout_seconds: float = 2.0,
+) -> str:
+    """Return a canonical public HTTPS push endpoint or fail closed."""
+    parsed = urlsplit(endpoint)
+    try:
+        port = parsed.port
+    except ValueError as error:
+        raise UnsafePushEndpoint(
+            "Endpoint must be a canonical public Web Push service URL"
+        ) from error
+    if (
+        parsed.scheme != "https"
+        or not parsed.hostname
+        or parsed.username is not None
+        or parsed.password is not None
+        or parsed.fragment
+        or port not in {None, 443}
+    ):
+        raise UnsafePushEndpoint("Endpoint must be a canonical public Web Push service URL")
+    try:
+        addresses = await asyncio.wait_for(
+            resolver(parsed.hostname, port or 443),
+            timeout=max(0.01, timeout_seconds),
+        )
+    except (OSError, asyncio.TimeoutError) as error:
+        raise UnsafePushEndpoint("Endpoint must resolve to a public Web Push service") from error
+    try:
+        public = addresses and all(ipaddress.ip_address(address).is_global for address in addresses)
+    except ValueError as error:
+        raise UnsafePushEndpoint("Endpoint must resolve to a public Web Push service") from error
+    if not public:
+        raise UnsafePushEndpoint("Endpoint must resolve to a public Web Push service")
+    return endpoint

src/push_notifications.py

@@ -6,6 +6,7 @@ from dataclasses import dataclass
 from typing import Awaitable, Callable
 
 from src.push_subscription_store import PushSubscriptionStore
+from src.push_endpoint_policy import UnsafePushEndpoint, validate_public_push_endpoint
 
 
 @dataclass(frozen=True)
@@ -22,8 +23,12 @@ class PushConfiguration:
 async def send_web_push(
     subscription: dict, payload: str, configuration: PushConfiguration
 ) -> None:
+    import requests
     from pywebpush import webpush
 
+    session = requests.Session()
+    session.max_redirects = 0
+
     await asyncio.to_thread(
         webpush,
         subscription_info=subscription,
@@ -31,6 +36,8 @@ async def send_web_push(
         vapid_private_key=configuration.private_key,
         vapid_claims={"sub": configuration.subject},
         ttl=300,
+        timeout=10,
+        requests_session=session,
     )
 
 
@@ -45,6 +52,7 @@ async def dispatch_unread_updates(
     send_timeout_seconds: float = 10.0,
     max_concurrency: int = 8,
     max_individual_notifications: int = 3,
+    endpoint_validator: Callable[[str], Awaitable[str]] | None = None,
 ) -> int:
     if not configuration.enabled:
         return 0
@@ -90,6 +98,15 @@ async def dispatch_unread_updates(
             async with semaphore:
                 if ownership_lost.is_set():
                     return 0
+                validate_endpoint = endpoint_validator
+                if validate_endpoint is None and send is None:
+                    validate_endpoint = validate_public_push_endpoint
+                try:
+                    if validate_endpoint is not None:
+                        await validate_endpoint(delivery.subscription["endpoint"])
+                except UnsafePushEndpoint:
+                    await asyncio.to_thread(store.delete_session, delivery.session_id)
+                    return 0
                 count = 0
                 digest_pending = set(delivery.digest_revisions)
                 new_revisions = tuple(

tests/test_push_endpoint_policy.py

@@ -0,0 +1,37 @@
+import pytest
+
+from src.push_endpoint_policy import UnsafePushEndpoint, validate_public_push_endpoint
+
+
+@pytest.mark.anyio
+@pytest.mark.parametrize(
+    "address",
+    ["127.0.0.1", "::1", "10.0.0.4", "169.254.169.254", "fc00::1"],
+)
+async def test_push_endpoint_rejects_every_non_public_resolved_address(address):
+    async def resolve(_host, _port):
+        return [address]
+
+    with pytest.raises(UnsafePushEndpoint, match="public Web Push service"):
+        await validate_public_push_endpoint(
+            "https://push.example/device", resolver=resolve
+        )
+
+
+@pytest.mark.anyio
+@pytest.mark.parametrize(
+    "endpoint",
+    [
+        "http://push.example/device",
+        "https://user@push.example/device",
+        "https://push.example:8443/device",
+        "https://push.example:not-a-port/device",
+        "https://push.example/device#fragment",
+    ],
+)
+async def test_push_endpoint_rejects_noncanonical_authorities_without_resolving(endpoint):
+    async def must_not_resolve(_host, _port):
+        raise AssertionError("invalid URL reached DNS")
+
+    with pytest.raises(UnsafePushEndpoint, match="canonical public Web Push"):
+        await validate_public_push_endpoint(endpoint, resolver=must_not_resolve)

tests/test_push_notifications.py

@@ -10,6 +10,15 @@ import pytest
 from src import dashboard_auth, gitea_proxy, main
 from src.push_notifications import PushConfiguration, dispatch_unread_updates
 from src.push_subscription_store import PushSubscriptionStore
+from src.push_endpoint_policy import UnsafePushEndpoint
+
+
+@pytest.fixture(autouse=True)
+def resolve_test_push_endpoints_publicly(monkeypatch):
+    async def accept(endpoint):
+        return endpoint
+
+    monkeypatch.setattr(main, "validate_public_push_endpoint", accept)
 
 
 def test_dispatch_lease_is_exclusive_recoverable_and_owner_fenced(tmp_path):
@@ -508,6 +517,32 @@ async def test_dispatch_removes_an_expired_push_endpoint(tmp_path):
     assert store.is_subscribed("session-a") is False
 
 
+@pytest.mark.anyio
+async def test_dispatch_removes_an_endpoint_that_rebinds_private_without_contacting_it(tmp_path):
+    store = PushSubscriptionStore(tmp_path / "push.sqlite3")
+    store.upsert("unsafe-device", {
+        "endpoint": "https://push.example/rebound",
+        "keys": {"p256dh": "public-key", "auth": "auth-secret"},
+    })
+    contacted = []
+
+    async def unread():
+        return {"items": [{"id": 8}]}
+
+    async def reject_rebound(_endpoint):
+        raise UnsafePushEndpoint("Endpoint must resolve to a public Web Push service")
+
+    async def send(subscription, _payload):
+        contacted.append(subscription["endpoint"])
+
+    config = PushConfiguration("public", "private", "mailto:ops@example.com")
+    assert await dispatch_unread_updates(
+        store, config, unread, send, endpoint_validator=reject_rebound
+    ) == 0
+    assert contacted == []
+    assert store.is_subscribed("unsafe-device") is False
+
+
 @pytest.mark.anyio
 async def test_transient_endpoint_failure_does_not_block_healthy_devices(tmp_path):
     store = PushSubscriptionStore(tmp_path / "push.sqlite3")
@@ -722,6 +757,37 @@ async def test_authenticated_device_can_subscribe_report_status_and_unsubscribe(
     assert (await main.push_status(request))["subscribed"] is False
 
 
+@pytest.mark.anyio
+async def test_subscription_rejects_an_unsafe_endpoint_before_persistence(tmp_path, monkeypatch):
+    store = PushSubscriptionStore(tmp_path / "push.sqlite3")
+    monkeypatch.setattr(main, "_push_subscription_store", store)
+    monkeypatch.setattr(
+        main, "_push_configuration",
+        lambda: PushConfiguration("public", "private", "mailto:ops@example.com"),
+    )
+
+    async def management_id(_session):
+        return "unsafe-device"
+
+    async def reject_private(_endpoint):
+        raise UnsafePushEndpoint("Endpoint must resolve to a public Web Push service")
+
+    monkeypatch.setattr(main.dashboard_auth, "session_management_id", management_id)
+    monkeypatch.setattr(main, "validate_public_push_endpoint", reject_private)
+    request = SimpleNamespace(state=SimpleNamespace(dashboard_session=object()))
+    payload = main.PushSubscriptionPayload(
+        endpoint="https://push.example/device-a",
+        keys={"p256dh": "public-key", "auth": "auth-secret"},
+    )
+
+    with pytest.raises(main.HTTPException) as rejected:
+        await main.subscribe_push(payload, request)
+
+    assert rejected.value.status_code == 422
+    assert rejected.value.detail == "Endpoint must resolve to a public Web Push service"
+    assert store.is_subscribed("unsafe-device") is False
+
+
 @pytest.mark.anyio
 async def test_subscription_baselines_every_revision_from_the_complete_snapshot(tmp_path, monkeypatch):
     store = PushSubscriptionStore(tmp_path / "push.sqlite3")