fix: harden LNURL refund destination checks and surface in-progress refunds

routstr/balance.py

@@ -367,6 +367,10 @@ async def refund_wallet_endpoint(
             return persisted
         if paid:
             return refund.describe(paid)
+        # Balance reads zero because a prior refund already debited it and is
+        # still settling; surface that as 409 rather than "no balance".
+        if await refund.latest_open(session, key):
+            raise refund.refund_in_progress_error()
 
     if key.reserved_balance > 0:
         # Release only durable reservations old enough to be stale. A newer

routstr/payment/lnurl.py

@@ -1,6 +1,9 @@
 from __future__ import annotations
 
+import asyncio
 import ipaddress
+import json
+import socket
 from collections.abc import Awaitable, Callable
 from typing import Any, TypedDict
 
@@ -48,15 +51,18 @@ class MeltOutcomeAmbiguousError(LNURLError):
 
 
 _MAX_LNURL_REDIRECTS = 3
+_MAX_LNURL_RESPONSE_BYTES = 64 * 1024
 _NON_PUBLIC_HOST_SUFFIXES = (".localhost", ".local", ".internal")
 
 
-def _require_public_https_destination(url: httpx.URL) -> None:
+async def _require_public_https_destination(url: httpx.URL) -> None:
     """Reject anything that is not a public HTTPS endpoint.
 
     LNURL destinations and their redirect targets are attacker-influenced, so
     every hop has to be re-checked: a single ``https://`` origin says nothing
-    about where a 302 points.
+    about where a 302 points. A bare hostname check is not enough either: a
+    public-looking name can resolve to a loopback/link-local/private address
+    (SSRF), so DNS is resolved here and every resulting address must be global.
     """
     if url.scheme != "https":
         raise LNURLError("LNURL destination must be an HTTPS URL")
@@ -66,15 +72,37 @@ def _require_public_https_destination(url: httpx.URL) -> None:
         raise LNURLError("LNURL destination has no host")
 
     try:
-        address = ipaddress.ip_address(host)
+        literal = ipaddress.ip_address(host)
     except ValueError:
-        if host == "localhost" or host.endswith(_NON_PUBLIC_HOST_SUFFIXES):
-            raise LNURLError("LNURL destination is not a public host") from None
+        literal = None
+
+    if literal is not None:
+        if not literal.is_global:
+            raise LNURLError("LNURL destination is not a public host")
         return
 
-    if not address.is_global:
+    if host == "localhost" or host.endswith(_NON_PUBLIC_HOST_SUFFIXES):
         raise LNURLError("LNURL destination is not a public host")
 
+    port = url.port or 443
+    try:
+        infos = await asyncio.get_running_loop().getaddrinfo(
+            host, port, proto=socket.IPPROTO_TCP
+        )
+    except socket.gaierror as e:
+        raise LNURLError("LNURL destination could not be resolved") from e
+    if not infos:
+        raise LNURLError("LNURL destination could not be resolved")
+    for info in infos:
+        try:
+            resolved = ipaddress.ip_address(info[4][0])
+        except ValueError as e:
+            raise LNURLError(
+                "LNURL destination resolved to an invalid address"
+            ) from e
+        if not resolved.is_global:
+            raise LNURLError("LNURL destination is not a public host")
+
 
 async def _fetch_lnurl_json(
     url: str, params: dict[str, int] | None = None
@@ -88,21 +116,34 @@ async def _fetch_lnurl_json(
         target = httpx.URL(url, params=params) if params else httpx.URL(url)
     except httpx.InvalidURL as e:
         raise LNURLError("LNURL destination is not a usable URL") from e
-    _require_public_https_destination(target)
+    await _require_public_https_destination(target)
 
+    raw: bytes | None = None
     async with httpx.AsyncClient() as client:
         for _ in range(_MAX_LNURL_REDIRECTS + 1):
-            response = await client.get(target, follow_redirects=False, timeout=10)
-            if not response.is_redirect:
-                break
-            target = target.join(response.headers.get("location", ""))
-            _require_public_https_destination(target)
+            async with client.stream(
+                "GET", target, follow_redirects=False, timeout=10
+            ) as response:
+                if response.is_redirect:
+                    target = target.join(response.headers.get("location", ""))
+                    await _require_public_https_destination(target)
+                    continue
+                response.raise_for_status()
+                chunks = bytearray()
+                async for chunk in response.aiter_bytes():
+                    chunks.extend(chunk)
+                    if len(chunks) > _MAX_LNURL_RESPONSE_BYTES:
+                        raise LNURLError("LNURL response exceeded the size limit")
+                raw = bytes(chunks)
+            break
         else:
             raise LNURLError("LNURL destination exceeded the redirect limit")
-        response.raise_for_status()
+
+    if raw is None:
+        raise LNURLError("LNURL destination exceeded the redirect limit")
 
     try:
-        data = response.json()
+        data = json.loads(raw)
     except ValueError as e:
         raise LNURLError("LNURL response was not valid JSON") from e
 
@@ -190,9 +231,10 @@ async def get_lnurl_data(lnurl: str) -> LNURLData:
     if not isinstance(callback_url, str):
         raise LNURLError("Invalid LNURL payRequest: missing callback URL")
     try:
-        _require_public_https_destination(httpx.URL(callback_url))
+        callback_target = httpx.URL(callback_url)
     except httpx.InvalidURL as e:
         raise LNURLError("Invalid LNURL callback URL") from e
+    await _require_public_https_destination(callback_target)
 
     min_sendable = lnurl_data.get("minSendable", 1000)  # Default 1 sat
     max_sendable = lnurl_data.get("maxSendable", 1000000000)  # Default 1000 BTC

routstr/refund.py

@@ -94,16 +94,7 @@ async def open_claim(
         await session.commit()
     except IntegrityError:
         await session.rollback()
-        raise HTTPException(
-            status_code=409,
-            detail={
-                "error": {
-                    "message": "A refund for this key is already in progress.",
-                    "type": "invalid_request_error",
-                    "code": "refund_in_progress",
-                }
-            },
-        )
+        raise refund_in_progress_error()
     return refund
 
 
@@ -205,6 +196,35 @@ async def hold(session: AsyncSession, refund: Refund, quote_id: str | None) -> N
     await session.commit()
 
 
+def refund_in_progress_error() -> HTTPException:
+    """The 409 raised when a key already has an in-flight refund claim."""
+    return HTTPException(
+        status_code=409,
+        detail={
+            "error": {
+                "message": "A refund for this key is already in progress.",
+                "type": "invalid_request_error",
+                "code": "refund_in_progress",
+            }
+        },
+    )
+
+
+async def latest_open(session: AsyncSession, key: ApiKey) -> Refund | None:
+    """Latest non-terminal (in-flight) claim for the key, if any.
+
+    An open claim means a prior refund already debited the balance and is still
+    settling, so the balance reads as zero even though a refund is under way.
+    """
+    result = await session.exec(
+        select(Refund)
+        .where(Refund.api_key_hashed_key == key.hashed_key)
+        .where(col(Refund.status).in_(REFUND_OPEN_STATUSES))
+        .order_by(col(Refund.created_at).desc(), col(Refund.updated_at).desc())
+    )
+    return result.first()
+
+
 async def latest_terminal(session: AsyncSession, key: ApiKey) -> Refund | None:
     """Latest paid refund of either method.
 

tests/integration/test_refund_claims.py

@@ -583,6 +583,32 @@ async def test_endpoint_refund_while_ambiguous_returns_409(
     assert (await _load_key(integration_session)).balance == 2_000_000
 
 
+@pytest.mark.asyncio
+async def test_endpoint_zero_balance_with_open_claim_returns_409(
+    integration_session: AsyncSession, patched_db_engine: None
+) -> None:
+    """A prior refund debited the balance and is still settling: the retry must
+    report refund_in_progress (409), not "no balance to refund" (400)."""
+    await _open_ambiguous(integration_session, "quote-123")
+    assert (await _load_key(integration_session)).balance == 0
+
+    send = AsyncMock()
+    with (
+        patch("routstr.refund.get_lnurl_data", AsyncMock()),
+        patch("routstr.refund.send_to_lnurl", send),
+    ):
+        with pytest.raises(HTTPException) as exc_info:
+            await refund_wallet_endpoint(
+                authorization=f"Bearer sk-{KEY_HASH}",
+                x_cashu=None,
+                session=integration_session,
+            )
+    assert exc_info.value.status_code == 409
+    assert isinstance(exc_info.value.detail, dict)
+    assert exc_info.value.detail["error"]["code"] == "refund_in_progress"
+    send.assert_not_awaited()
+
+
 @pytest.mark.asyncio
 async def test_cashu_token_survives_failed_ledger_write(
     integration_session: AsyncSession, patched_db_engine: None

tests/unit/test_lnurl_amount_and_destination.py

@@ -6,6 +6,7 @@ is what stops a pre-dispatch failure from stranding proofs.
 """
 
 import math
+import socket
 from collections.abc import Callable
 from typing import Any
 from unittest.mock import AsyncMock, MagicMock, patch
@@ -347,6 +348,61 @@ async def test_send_to_lnurl_does_not_reserve_before_lnurl_validation() -> None:
     assert raw_send.await_args.kwargs["amount"] == 1000
 
 
+def _patch_getaddrinfo(ip: str) -> Any:
+    """Force DNS resolution of any hostname to a single fixed IP."""
+
+    async def fake_getaddrinfo(host: str, port: int, **_kw: object) -> list[Any]:
+        return [
+            (socket.AF_INET, socket.SOCK_STREAM, socket.IPPROTO_TCP, "", (ip, port))
+        ]
+
+    loop = MagicMock()
+    loop.getaddrinfo = fake_getaddrinfo
+    return patch.object(
+        lnurl_module.asyncio, "get_running_loop", return_value=loop
+    )
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    "private_ip", ["127.0.0.1", "10.0.0.5", "169.254.169.254", "192.168.1.1"]
+)
+async def test_guard_rejects_public_hostname_resolving_to_private(
+    private_ip: str,
+) -> None:
+    """A public-looking name must be rejected when DNS points it inward (SSRF)."""
+    with (
+        _patch_getaddrinfo(private_ip),
+        pytest.raises(LNURLError, match="public host"),
+    ):
+        await lnurl_module._require_public_https_destination(
+            httpx.URL("https://totally-public.example.com/cb")
+        )
+
+
+@pytest.mark.asyncio
+async def test_guard_allows_public_hostname_resolving_to_public() -> None:
+    with _patch_getaddrinfo("93.184.216.34"):
+        await lnurl_module._require_public_https_destination(
+            httpx.URL("https://totally-public.example.com/cb")
+        )
+
+
+@pytest.mark.asyncio
+async def test_get_lnurl_data_rejects_oversized_response() -> None:
+    big = b"x" * (lnurl_module._MAX_LNURL_RESPONSE_BYTES + 1)
+
+    def handler(_request: httpx.Request) -> httpx.Response:
+        return httpx.Response(200, content=big)
+
+    with (
+        _patch_getaddrinfo("93.184.216.34"),
+        _mock_client(handler),
+        pytest.raises(LNURLError, match="size limit"),
+    ):
+        await get_lnurl_data("owner@ln.tld")
+
+
 def test_select_melt_proofs_ignores_fees_for_unneeded_wallet_proofs() -> None:
     from routstr.payment.lnurl import _select_melt_proofs