CVE-2026-27696 - Server-Side Request Forgery (SSRF) via Watch URLs, set env var ALLOW_IANA_RESTRICTED_ADDRESSES to true to access IANA reserved URLs such as http://169.254.169.254, http://10.0.0.1/, http://127.0.0.1/, etc.

dgtlmoon · dgtlmoon · commit fe7aa38c651d · 2026-02-23T21:56:43.000+01:00
diff --git a/changedetectionio/content_fetchers/requests.py b/changedetectionio/content_fetchers/requests.py
@@ -1,4 +1,5 @@
 from loguru import logger
+from urllib.parse import urljoin, urlparse
 import hashlib
 import os
 import re
@@ -7,6 +8,7 @@
 from changedetectionio import strtobool
 from changedetectionio.content_fetchers.exceptions import BrowserStepsInUnsupportedFetcher, EmptyReply, Non200ErrorCodeReceived
 from changedetectionio.content_fetchers.base import Fetcher
+from changedetectionio.validate_url import is_private_hostname
 
 
 # "html_requests" is listed as the default fetcher in store.py!
@@ -79,14 +81,48 @@ def _run_sync(self,
         if strtobool(os.getenv('ALLOW_FILE_URI', 'false')) and url.startswith('file://'):
             from requests_file import FileAdapter
             session.mount('file://', FileAdapter())
+
+        allow_iana_restricted = strtobool(os.getenv('ALLOW_IANA_RESTRICTED_ADDRESSES', 'false'))
+
         try:
+            # Fresh DNS check at fetch time — catches DNS rebinding regardless of add-time cache.
+            if not allow_iana_restricted:
+                parsed_initial = urlparse(url)
+                if parsed_initial.hostname and is_private_hostname(parsed_initial.hostname):
+                    raise Exception(f"Fetch blocked: '{url}' resolves to a private/reserved IP address. "
+                                    f"Set ALLOW_IANA_RESTRICTED_ADDRESSES=true to allow.")
+
             r = session.request(method=request_method,
                                 data=request_body.encode('utf-8') if type(request_body) is str else request_body,
                                 url=url,
                                 headers=request_headers,
                                 timeout=timeout,
                                 proxies=proxies,
-                                verify=False)
+                                verify=False,
+                                allow_redirects=False)
+
+            # Manually follow redirects so each hop's resolved IP can be validated,
+            # preventing SSRF via an open redirect on a public host.
+            current_url = url
+            for _ in range(10):
+                if not r.is_redirect:
+                    break
+                location = r.headers.get('Location', '')
+                redirect_url = urljoin(current_url, location)
+                if not allow_iana_restricted:
+                    parsed_redirect = urlparse(redirect_url)
+                    if parsed_redirect.hostname and is_private_hostname(parsed_redirect.hostname):
+                        raise Exception(f"Redirect blocked: '{redirect_url}' resolves to a private/reserved IP address.")
+                current_url = redirect_url
+                r = session.request('GET', redirect_url,
+                                    headers=request_headers,
+                                    timeout=timeout,
+                                    proxies=proxies,
+                                    verify=False,
+                                    allow_redirects=False)
+            else:
+                raise Exception("Too many redirects")
+
         except Exception as e:
             msg = str(e)
             if proxies and 'SOCKSHTTPSConnectionPool' in msg:
diff --git a/changedetectionio/run_basic_tests.sh b/changedetectionio/run_basic_tests.sh
@@ -44,12 +44,12 @@ data_sanity_test () {
   cd ..
   TMPDIR=$(mktemp -d)
   PORT_N=$((5000 + RANDOM % (6501 - 5000)))
-  ./changedetection.py -p $PORT_N -d $TMPDIR -u "https://localhost?test-url-is-sanity=1" &
+  ALLOW_IANA_RESTRICTED_ADDRESSES=true ./changedetection.py -p $PORT_N -d $TMPDIR -u "https://localhost?test-url-is-sanity=1" &
   PID=$!
   sleep 5
   kill $PID
   sleep 2
-  ./changedetection.py -p $PORT_N -d $TMPDIR &
+  ALLOW_IANA_RESTRICTED_ADDRESSES=true ./changedetection.py -p $PORT_N -d $TMPDIR &
   PID=$!
   sleep 5
   # On a restart the URL should still be there
diff --git a/changedetectionio/store/__init__.py b/changedetectionio/store/__init__.py
@@ -728,8 +728,11 @@ def add_watch(self, url, tag='', extras=None, tag_uuids=None, save_immediately=T
                 return False
 
         if not is_safe_valid_url(url):
-            flash(gettext('Watch protocol is not permitted or invalid URL format'), 'error')
-
+            from flask import has_request_context
+            if has_request_context():
+                flash(gettext('Watch protocol is not permitted or invalid URL format'), 'error')
+            else:
+                logger.error(f"add_watch: URL '{url}' is not permitted or invalid, skipping.")
             return None
 
         # Check PAGE_WATCH_LIMIT if set
diff --git a/changedetectionio/tests/conftest.py b/changedetectionio/tests/conftest.py
@@ -13,6 +13,10 @@
 # When test server is slow/unresponsive, workers fail fast instead of holding UUIDs for 45s
 # This prevents exponential priority growth from repeated deferrals (priority × 10 each defer)
 os.environ['DEFAULT_SETTINGS_REQUESTS_TIMEOUT'] = '5'
+# Test server runs on localhost (127.0.0.1) which is a private IP.
+# Allow it globally so all existing tests keep working; test_ssrf_protection
+# uses monkeypatch to temporarily override this for its own assertions.
+os.environ['ALLOW_IANA_RESTRICTED_ADDRESSES'] = 'true'
 
 from changedetectionio.flask_app import init_app_secret, changedetection_app
 from changedetectionio.tests.util import live_server_setup, new_live_server_setup
diff --git a/changedetectionio/tests/test_security.py b/changedetectionio/tests/test_security.py
@@ -1,4 +1,5 @@
 import os
+import pytest
 
 from flask import url_for
 
@@ -579,3 +580,131 @@ def test_static_directory_traversal(client, live_server, measure_memory_usage, d
     # Should get 403 (not authenticated) or 404 (file not found), not a path traversal
     assert res.status_code in [403, 404]
 
+
+def test_ssrf_private_ip_blocked(client, live_server, monkeypatch, measure_memory_usage, datastore_path):
+    """
+    SSRF protection: IANA-reserved/private IP addresses must be blocked by default.
+
+    Covers:
+    1. is_private_hostname() correctly classifies all reserved ranges
+    2. is_safe_valid_url() rejects private-IP URLs at add-time (env var off)
+    3. is_safe_valid_url() allows private-IP URLs when ALLOW_IANA_RESTRICTED_ADDRESSES=true
+    4. UI form rejects private-IP URLs and shows the standard error message
+    5. Requests fetcher blocks fetch-time DNS rebinding (fresh check on every fetch)
+    6. Requests fetcher blocks redirects that lead to a private IP (open-redirect bypass)
+
+    conftest.py sets ALLOW_IANA_RESTRICTED_ADDRESSES=true globally so the test
+    server (localhost) keeps working for all other tests.  monkeypatch temporarily
+    overrides it to 'false' here, and is automatically restored after the test.
+    """
+    from unittest.mock import patch, MagicMock
+    from changedetectionio.validate_url import is_safe_valid_url, is_private_hostname
+
+    monkeypatch.setenv('ALLOW_IANA_RESTRICTED_ADDRESSES', 'false')
+    # Clear any URL results cached while the env var was 'true'
+    is_safe_valid_url.cache_clear()
+
+    # ------------------------------------------------------------------
+    # 1. is_private_hostname() — unit tests across all reserved ranges
+    # ------------------------------------------------------------------
+    private_hosts = [
+        '127.0.0.1',          # loopback
+        '10.0.0.1',           # RFC 1918
+        '172.16.0.1',         # RFC 1918
+        '192.168.1.1',        # RFC 1918
+        '169.254.169.254',    # link-local / AWS metadata endpoint
+        '::1',                # IPv6 loopback
+        'fc00::1',            # IPv6 unique local
+        'fe80::1',            # IPv6 link-local
+    ]
+    for host in private_hosts:
+        assert is_private_hostname(host), f"{host} should be identified as private/reserved"
+
+    for host in ['8.8.8.8', '1.1.1.1']:
+        assert not is_private_hostname(host), f"{host} should be identified as public"
+
+    # ------------------------------------------------------------------
+    # 2. is_safe_valid_url() blocks private-IP URLs (env var off)
+    # ------------------------------------------------------------------
+    blocked_urls = [
+        'http://127.0.0.1/',
+        'http://10.0.0.1/',
+        'http://172.16.0.1/',
+        'http://192.168.1.1/',
+        'http://169.254.169.254/',
+        'http://169.254.169.254/latest/meta-data/iam/security-credentials/',
+        'http://[::1]/',
+        'http://[fc00::1]/',
+        'http://[fe80::1]/',
+    ]
+    for url in blocked_urls:
+        assert not is_safe_valid_url(url), f"{url} should be blocked by is_safe_valid_url"
+
+    # ------------------------------------------------------------------
+    # 3. ALLOW_IANA_RESTRICTED_ADDRESSES=true bypasses the block
+    # ------------------------------------------------------------------
+    monkeypatch.setenv('ALLOW_IANA_RESTRICTED_ADDRESSES', 'true')
+    is_safe_valid_url.cache_clear()
+    assert is_safe_valid_url('http://127.0.0.1/'), \
+        "Private IP should be allowed when ALLOW_IANA_RESTRICTED_ADDRESSES=true"
+
+    # Restore the block for the remaining assertions
+    monkeypatch.setenv('ALLOW_IANA_RESTRICTED_ADDRESSES', 'false')
+    is_safe_valid_url.cache_clear()
+
+    # ------------------------------------------------------------------
+    # 4. UI form rejects private-IP URLs
+    # ------------------------------------------------------------------
+    for url in ['http://127.0.0.1/', 'http://169.254.169.254/latest/meta-data/']:
+        res = client.post(
+            url_for('ui.ui_views.form_quick_watch_add'),
+            data={'url': url, 'tags': ''},
+            follow_redirects=True
+        )
+        assert b'Watch protocol is not permitted or invalid URL format' in res.data, \
+            f"UI should reject {url}"
+
+    # ------------------------------------------------------------------
+    # 5. Fetch-time DNS-rebinding check in the requests fetcher
+    #    Simulates: URL passed add-time validation with a public IP, but
+    #    by fetch time DNS has been rebound to a private IP.
+    # ------------------------------------------------------------------
+    from changedetectionio.content_fetchers.requests import fetcher as RequestsFetcher
+
+    f = RequestsFetcher()
+
+    with patch('changedetectionio.content_fetchers.requests.is_private_hostname', return_value=True):
+        with pytest.raises(Exception, match='private/reserved'):
+            f._run_sync(
+                url='http://example.com/',
+                timeout=5,
+                request_headers={},
+                request_body=None,
+                request_method='GET',
+            )
+
+    # ------------------------------------------------------------------
+    # 6. Redirect-to-private-IP blocked (open-redirect SSRF bypass)
+    #    Public host returns a 302 pointing at an IANA-reserved address.
+    # ------------------------------------------------------------------
+    mock_redirect = MagicMock()
+    mock_redirect.is_redirect = True
+    mock_redirect.status_code = 302
+    mock_redirect.headers = {'Location': 'http://169.254.169.254/latest/meta-data/'}
+
+    def _private_only_for_redirect(hostname):
+        # Initial host is "public"; the redirect target is private
+        return hostname in {'169.254.169.254', '10.0.0.1', '172.16.0.1',
+                            '192.168.0.1', '127.0.0.1', '::1'}
+
+    with patch('changedetectionio.content_fetchers.requests.is_private_hostname',
+               side_effect=_private_only_for_redirect):
+        with patch('requests.Session.request', return_value=mock_redirect):
+            with pytest.raises(Exception, match='Redirect blocked'):
+                f._run_sync(
+                    url='http://example.com/',
+                    timeout=5,
+                    request_headers={},
+                    request_body=None,
+                    request_method='GET',
+                )
diff --git a/changedetectionio/validate_url.py b/changedetectionio/validate_url.py
@@ -1,3 +1,5 @@
+import ipaddress
+import socket
 from functools import lru_cache
 from loguru import logger
 from urllib.parse import urlparse, urlunparse, parse_qsl, urlencode
@@ -56,6 +58,23 @@ def normalize_url_encoding(url):
         return url
 
 
+def is_private_hostname(hostname):
+    """Return True if hostname resolves to an IANA-restricted (private/reserved) IP address.
+
+    Fails closed: unresolvable hostnames return True (block them).
+    Never cached — callers that need fresh DNS resolution (e.g. at fetch time) can call
+    this directly without going through the lru_cached is_safe_valid_url().
+    """
+    try:
+        for info in socket.getaddrinfo(hostname, None):
+            ip = ipaddress.ip_address(info[4][0])
+            if ip.is_private or ip.is_loopback or ip.is_link_local or ip.is_reserved:
+                return True
+    except socket.gaierror:
+        return True
+    return False
+
+
 @lru_cache(maxsize=10000)
 def is_safe_valid_url(test_url):
     from changedetectionio import strtobool
@@ -119,4 +138,12 @@ def is_safe_valid_url(test_url):
         logger.warning(f'URL f"{test_url}" failed validation, aborting.')
         return False
 
+    # Block IANA-restricted (private/reserved) IP addresses unless explicitly allowed.
+    # This is an add-time check; fetch-time re-validation in requests.py handles DNS rebinding.
+    if not strtobool(os.getenv('ALLOW_IANA_RESTRICTED_ADDRESSES', 'false')):
+        parsed = urlparse(test_url)
+        if parsed.hostname and is_private_hostname(parsed.hostname):
+            logger.warning(f'URL "{test_url}" resolves to a private/reserved IP address, aborting.')
+            return False
+
     return True
