Restrict torrent prefetch to trusted origins (#976)

shelfmark/download/clients/torrent_utils.py

@@ -7,12 +7,13 @@ import hashlib
 import re
 from binascii import Error as BinasciiError
 from dataclasses import dataclass
-from urllib.parse import parse_qs, urljoin, urlparse
+from urllib.parse import ParseResult, parse_qs, urljoin, urlparse
 
 import requests
 
 from shelfmark.core.config import config
 from shelfmark.core.logger import setup_logger
+from shelfmark.core.utils import normalize_http_url
 from shelfmark.download.network import get_ssl_verify
 
 logger = setup_logger(__name__)
@@ -32,6 +33,7 @@ _TORRENT_FETCH_ERRORS = (
     ValueError,
 )
 _TORRENT_PARSE_ERRORS = (IndexError, KeyError, TypeError, ValueError)
+_TRUSTED_TORRENT_FETCH_URL_CONFIG_KEYS = ("PROWLARR_URL", "NEWZNAB_URL")
 
 type BencodeValue = dict[str | bytes, BencodeValue] | list[BencodeValue] | int | bytes | str
 
@@ -93,6 +95,9 @@ def extract_torrent_info(
     # Not a magnet - try to fetch and parse the .torrent file
     if not fetch_torrent:
         return TorrentInfo(info_hash=expected_hash, torrent_data=None, is_magnet=False)
+    if not _is_trusted_torrent_fetch_url(url):
+        logger.debug("Skipping torrent prefetch for untrusted URL: %s...", url[:80])
+        return TorrentInfo(info_hash=expected_hash, torrent_data=None, is_magnet=False)
 
     headers: dict[str, str] = {"Accept": "application/x-bittorrent"}
     # TODO(shelfmark): Move this source-specific Prowlarr auth handling into a source hook.
@@ -133,6 +138,12 @@ def extract_torrent_info(
                     is_magnet=True,
                     magnet_url=redirect_url,
                 )
+            if not _is_trusted_torrent_fetch_url(redirect_url):
+                logger.debug(
+                    "Skipping torrent prefetch redirect to untrusted URL: %s...",
+                    redirect_url[:80],
+                )
+                return TorrentInfo(info_hash=expected_hash, torrent_data=None, is_magnet=False)
             # Not a magnet redirect, follow it manually
             logger.debug("Following redirect to: %s...", redirect_url[:80])
             resp = requests.get(
@@ -172,6 +183,36 @@ def extract_torrent_info(
         return TorrentInfo(info_hash=expected_hash, torrent_data=None, is_magnet=False)
 
 
+def _is_trusted_torrent_fetch_url(url: str) -> bool:
+    parsed = urlparse(url)
+    origin = _url_origin(parsed)
+    if origin is None:
+        return False
+
+    for key in _TRUSTED_TORRENT_FETCH_URL_CONFIG_KEYS:
+        configured_url = str(config.get(key, "") or "").strip()
+        if not configured_url:
+            continue
+        configured_origin = _url_origin(urlparse(normalize_http_url(configured_url)))
+        if configured_origin == origin:
+            return True
+
+    return False
+
+
+def _url_origin(parsed_url: ParseResult) -> tuple[str, str, int] | None:
+    scheme = parsed_url.scheme.lower()
+    if scheme not in {"http", "https"}:
+        return None
+
+    hostname = parsed_url.hostname
+    if not hostname:
+        return None
+
+    default_port = 443 if scheme == "https" else 80
+    return (scheme, hostname.lower(), parsed_url.port or default_port)
+
+
 def parse_transmission_url(url: str) -> tuple[str, str, int, str]:
     """Parse Transmission URL into (protocol, host, port, path)."""
     parsed = urlparse(url)

tests/prowlarr/test_torrent_utils.py

@@ -10,6 +10,7 @@ Tests:
 
 import base64
 import hashlib
+from unittest.mock import MagicMock
 
 import pytest
 
@@ -18,6 +19,7 @@ from shelfmark.download.clients.torrent_utils import (
     bencode_encode,
     extract_hash_from_magnet,
     extract_info_hash_from_torrent,
+    extract_torrent_info,
     parse_transmission_url,
 )
 
@@ -356,6 +358,121 @@ class TestExtractInfoHash:
         assert extract_info_hash_from_torrent(torrent_bytes) == expected
 
 
+class TestExtractTorrentInfo:
+    """Tests for extracting torrent info from user-supplied URLs."""
+
+    def test_does_not_fetch_untrusted_http_torrent_url(self, monkeypatch):
+        """Arbitrary HTTP torrent URLs are passed through without backend prefetch."""
+        expected_hash = "3b245504cf5f11bbdbe1201cea6a6bf45aee1bc0"
+        monkeypatch.setattr(
+            "shelfmark.download.clients.torrent_utils.config.get",
+            lambda key, default="": "",
+        )
+        mock_get = MagicMock()
+        monkeypatch.setattr("shelfmark.download.clients.torrent_utils.requests.get", mock_get)
+
+        result = extract_torrent_info(
+            "https://attacker.example/book.torrent",
+            fetch_torrent=True,
+            expected_hash=expected_hash,
+        )
+
+        assert result.info_hash == expected_hash
+        assert result.torrent_data is None
+        assert result.is_magnet is False
+        mock_get.assert_not_called()
+
+    def test_fetches_configured_prowlarr_torrent_url(self, monkeypatch):
+        """Configured Prowlarr download URLs can still be prefetched and parsed."""
+        info_dict = {
+            b"name": b"trusted.txt",
+            b"length": 100,
+            b"piece length": 16384,
+            b"pieces": b"\x00" * 20,
+        }
+        torrent_data = bencode_encode({b"info": info_dict})
+        expected_hash = hashlib.sha1(bencode_encode(info_dict)).hexdigest().lower()
+
+        config_values = {
+            "PROWLARR_URL": "https://prowlarr.example",
+            "PROWLARR_API_KEY": "secret",
+        }
+        monkeypatch.setattr(
+            "shelfmark.download.clients.torrent_utils.config.get",
+            lambda key, default="": config_values.get(key, default),
+        )
+        response = MagicMock(status_code=200, content=torrent_data)
+        response.raise_for_status = MagicMock()
+        mock_get = MagicMock(return_value=response)
+        monkeypatch.setattr("shelfmark.download.clients.torrent_utils.requests.get", mock_get)
+
+        result = extract_torrent_info(
+            "https://prowlarr.example/1/download?apikey=secret&indexer=7",
+            fetch_torrent=True,
+        )
+
+        assert result.info_hash == expected_hash
+        assert result.torrent_data == torrent_data
+        assert result.is_magnet is False
+        mock_get.assert_called_once()
+
+    def test_normalizes_configured_origin_before_trusting_torrent_url(self, monkeypatch):
+        """Configured Prowlarr URLs match the same normalization used by the source."""
+        info_dict = {
+            b"name": b"trusted.txt",
+            b"length": 100,
+            b"piece length": 16384,
+            b"pieces": b"\x00" * 20,
+        }
+        torrent_data = bencode_encode({b"info": info_dict})
+        expected_hash = hashlib.sha1(bencode_encode(info_dict)).hexdigest().lower()
+
+        config_values = {
+            "PROWLARR_URL": "prowlarr.example:9696/",
+            "PROWLARR_API_KEY": "secret",
+        }
+        monkeypatch.setattr(
+            "shelfmark.download.clients.torrent_utils.config.get",
+            lambda key, default="": config_values.get(key, default),
+        )
+        response = MagicMock(status_code=200, content=torrent_data)
+        response.raise_for_status = MagicMock()
+        mock_get = MagicMock(return_value=response)
+        monkeypatch.setattr("shelfmark.download.clients.torrent_utils.requests.get", mock_get)
+
+        result = extract_torrent_info(
+            "http://prowlarr.example:9696/1/download?apikey=secret&indexer=7",
+            fetch_torrent=True,
+        )
+
+        assert result.info_hash == expected_hash
+        assert result.torrent_data == torrent_data
+        mock_get.assert_called_once()
+
+    def test_does_not_follow_trusted_torrent_url_redirect_to_untrusted_host(self, monkeypatch):
+        """Trusted HTTP prefetch does not continue through arbitrary redirects."""
+        expected_hash = "3b245504cf5f11bbdbe1201cea6a6bf45aee1bc0"
+        monkeypatch.setattr(
+            "shelfmark.download.clients.torrent_utils.config.get",
+            lambda key, default="": "https://prowlarr.example" if key == "PROWLARR_URL" else "",
+        )
+        response = MagicMock(status_code=302)
+        response.headers = {"Location": "https://attacker.example/book.torrent"}
+        mock_get = MagicMock(return_value=response)
+        monkeypatch.setattr("shelfmark.download.clients.torrent_utils.requests.get", mock_get)
+
+        result = extract_torrent_info(
+            "https://prowlarr.example/1/download?apikey=secret&indexer=7",
+            fetch_torrent=True,
+            expected_hash=expected_hash,
+        )
+
+        assert result.info_hash == expected_hash
+        assert result.torrent_data is None
+        assert result.is_magnet is False
+        mock_get.assert_called_once()
+
+
 class TestExtractHashFromMagnet:
     """Tests for extracting hash from magnet links."""