fix(sabnzbd): strip Prowlarr API key on cross-host NZB redirects (#1424)

_fetch_nzb_content sent X-Api-Key
then followed redirects with the header still attached, leaking the
Prowlarr key when Prowlarr 302s to the indexer download link. Follow
redirects manually with allow_redirects=False and re-evaluate headers
 per hop, mirroring the torrent path.

shelfmark/download/clients/sabnzbd.py

@@ -5,7 +5,7 @@ Uses SABnzbd's REST API directly via requests (no external dependency).
 
 import ipaddress
 from typing import Any
-from urllib.parse import urlparse
+from urllib.parse import urljoin, urlparse
 
 import requests
 from publicsuffixlist import PublicSuffixList
@@ -34,6 +34,7 @@ _SABNZBD_CLIENT_ERRORS = (
 )
 _SabnzbdRequestParam = str | int | float | bool
 _PUBLIC_SUFFIXES = PublicSuffixList()
+_NZB_FETCH_MAX_REDIRECTS = 5
 
 
 def _url_origin(value: str) -> tuple[str, str, int] | None:
@@ -266,10 +267,34 @@ class SABnzbdClient(DownloadClient):
 
     def _fetch_nzb_content(self, url: str) -> bytes:
         """Fetch NZB content, including Prowlarr auth headers when appropriate."""
-        headers = self._get_prowlarr_headers(url)
-        response = requests.get(url, timeout=30, headers=headers, verify=get_ssl_verify(url))
-        response.raise_for_status()
-        return response.content
+        # Follow redirects manually so the Prowlarr API key is re-evaluated
+        # per hop. requests forwards custom headers such as X-Api-Key to the
+        # redirect target even when it is a different host, so letting it
+        # follow a Prowlarr 302 to the indexer's own download link would leak
+        # the key to a third party. This mirrors the torrent fetch path.
+        current_url = url
+        redirects_remaining = _NZB_FETCH_MAX_REDIRECTS
+        while True:
+            headers = self._get_prowlarr_headers(current_url)
+            response = requests.get(
+                current_url,
+                timeout=30,
+                headers=headers,
+                verify=get_ssl_verify(current_url),
+                allow_redirects=False,
+            )
+            if response.status_code not in (301, 302, 303, 307, 308):
+                response.raise_for_status()
+                return response.content
+            location = response.headers.get("Location", "")
+            if not location:
+                response.raise_for_status()
+                return response.content
+            if redirects_remaining <= 0:
+                msg = f"Too many redirects fetching NZB from {urlparse(url).hostname or 'url'}"
+                raise requests.exceptions.TooManyRedirects(msg)
+            redirects_remaining -= 1
+            current_url = urljoin(current_url, location)
 
     def _can_prefetch_nzb_url(self, url: str) -> bool:
         target_origin = _url_origin(url)

tests/prowlarr/test_sabnzbd_client.py

@@ -730,6 +730,58 @@ class TestSABnzbdClientAddDownload:
         assert SABnzbdClient()._can_prefetch_nzb_url(nzb_url) is expected
 
 
+class TestFetchNzbContentRedirects:
+    """_fetch_nzb_content must not leak the Prowlarr API key across hosts."""
+
+    @staticmethod
+    def _client(monkeypatch):
+        config_values = {
+            "SABNZBD_URL": "http://localhost:8080",
+            "SABNZBD_API_KEY": "abc123",
+            "PROWLARR_URL": "https://prowlarr.example",
+            "PROWLARR_API_KEY": "secret",
+        }
+        monkeypatch.setattr(
+            "shelfmark.download.clients.sabnzbd.config.get",
+            lambda key, default="": config_values.get(key, default),
+        )
+        from shelfmark.download.clients.sabnzbd import SABnzbdClient
+
+        with patch.object(SABnzbdClient, "__init__", lambda x: None):
+            client = SABnzbdClient()
+        return client
+
+    def test_strips_api_key_on_cross_host_redirect(self, monkeypatch):
+        """Prowlarr often 302s to the indexer's own download link."""
+        client = self._client(monkeypatch)
+        redirect = MagicMock(
+            status_code=302, headers={"Location": "https://indexer.example/get.nzb"}
+        )
+        final = MagicMock(status_code=200, content=b"nzbdata")
+        with patch(
+            "shelfmark.download.clients.sabnzbd.requests.get",
+            MagicMock(side_effect=[redirect, final]),
+        ) as mock_get:
+            assert client._fetch_nzb_content("https://prowlarr.example/download?id=1") == b"nzbdata"
+        assert mock_get.call_count == 2
+        assert mock_get.call_args_list[0].kwargs["headers"].get("X-Api-Key") == "secret"
+        assert "X-Api-Key" not in mock_get.call_args_list[1].kwargs["headers"]
+        assert mock_get.call_args_list[0].kwargs.get("allow_redirects") is False
+
+    def test_keeps_api_key_on_same_host_redirect(self, monkeypatch):
+        client = self._client(monkeypatch)
+        redirect = MagicMock(status_code=302, headers={"Location": "/download2?id=1"})
+        final = MagicMock(status_code=200, content=b"nzbdata")
+        with patch(
+            "shelfmark.download.clients.sabnzbd.requests.get",
+            MagicMock(side_effect=[redirect, final]),
+        ) as mock_get:
+            assert client._fetch_nzb_content("https://prowlarr.example/download?id=1") == b"nzbdata"
+        assert mock_get.call_count == 2
+        assert mock_get.call_args_list[1].args[0] == "https://prowlarr.example/download2?id=1"
+        assert mock_get.call_args_list[1].kwargs["headers"].get("X-Api-Key") == "secret"
+
+
 class TestSABnzbdClientRemove:
     """Tests for SABnzbdClient.remove()."""