| From d01648738934922d413b65f2f97951cbab66e0bd Mon Sep 17 00:00:00 2001 |
| From: "Gregory P. Smith" <greg@krypto.org> |
| Date: Tue, 21 Jun 2022 13:16:57 -0700 |
| Subject: [PATCH] gh-87389: Fix an open redirection vulnerability in |
| http.server. (GH-93879) |
| |
| Fix an open redirection vulnerability in the `http.server` module when |
| an URI path starts with `//` that could produce a 301 Location header |
| with a misleading target. Vulnerability discovered, and logic fix |
| proposed, by Hamza Avvan (@hamzaavvan). |
| |
| Test and comments authored by Gregory P. Smith [Google]. |
| (cherry picked from commit 4abab6b603dd38bec1168e9a37c40a48ec89508e) |
| |
| Co-authored-by: Gregory P. Smith <greg@krypto.org> |
| --- |
| Lib/http/server.py | 7 +++ |
| Lib/test/test_httpservers.py | 53 ++++++++++++++++++- |
| ...2-06-15-20-09-23.gh-issue-87389.QVaC3f.rst | 3 ++ |
| 3 files changed, 61 insertions(+), 2 deletions(-) |
| create mode 100644 Misc/NEWS.d/next/Security/2022-06-15-20-09-23.gh-issue-87389.QVaC3f.rst |
| |
| diff --git a/Lib/http/server.py b/Lib/http/server.py |
| index 38f7accad7a3..39de35458c38 100644 |
| --- a/Lib/http/server.py |
| +++ b/Lib/http/server.py |
| @@ -332,6 +332,13 @@ def parse_request(self): |
| return False |
| self.command, self.path = command, path |
| |
| + # gh-87389: The purpose of replacing '//' with '/' is to protect |
| + # against open redirect attacks possibly triggered if the path starts |
| + # with '//' because http clients treat //path as an absolute URI |
| + # without scheme (similar to http://path) rather than a path. |
| + if self.path.startswith('//'): |
| + self.path = '/' + self.path.lstrip('/') # Reduce to a single / |
| + |
| # Examine the headers and look for a Connection directive. |
| try: |
| self.headers = http.client.parse_headers(self.rfile, |
| diff --git a/Lib/test/test_httpservers.py b/Lib/test/test_httpservers.py |
| index 87d4924a34b3..fb026188f0b4 100644 |
| --- a/Lib/test/test_httpservers.py |
| +++ b/Lib/test/test_httpservers.py |
| @@ -330,7 +330,7 @@ class request_handler(NoLogRequestHandler, SimpleHTTPRequestHandler): |
| pass |
| |
| def setUp(self): |
| - BaseTestCase.setUp(self) |
| + super().setUp() |
| self.cwd = os.getcwd() |
| basetempdir = tempfile.gettempdir() |
| os.chdir(basetempdir) |
| @@ -358,7 +358,7 @@ def tearDown(self): |
| except: |
| pass |
| finally: |
| - BaseTestCase.tearDown(self) |
| + super().tearDown() |
| |
| def check_status_and_reason(self, response, status, data=None): |
| def close_conn(): |
| @@ -414,6 +414,55 @@ def test_undecodable_filename(self): |
| self.check_status_and_reason(response, HTTPStatus.OK, |
| data=support.TESTFN_UNDECODABLE) |
| |
| + def test_get_dir_redirect_location_domain_injection_bug(self): |
| + """Ensure //evil.co/..%2f../../X does not put //evil.co/ in Location. |
| + |
| + //netloc/ in a Location header is a redirect to a new host. |
| + https://github.com/python/cpython/issues/87389 |
| + |
| + This checks that a path resolving to a directory on our server cannot |
| + resolve into a redirect to another server. |
| + """ |
| + os.mkdir(os.path.join(self.tempdir, 'existing_directory')) |
| + url = f'/python.org/..%2f..%2f..%2f..%2f..%2f../%0a%0d/../{self.tempdir_name}/existing_directory' |
| + expected_location = f'{url}/' # /python.org.../ single slash single prefix, trailing slash |
| + # Canonicalizes to /tmp/tempdir_name/existing_directory which does |
| + # exist and is a dir, triggering the 301 redirect logic. |
| + response = self.request(url) |
| + self.check_status_and_reason(response, HTTPStatus.MOVED_PERMANENTLY) |
| + location = response.getheader('Location') |
| + self.assertEqual(location, expected_location, msg='non-attack failed!') |
| + |
| + # //python.org... multi-slash prefix, no trailing slash |
| + attack_url = f'/{url}' |
| + response = self.request(attack_url) |
| + self.check_status_and_reason(response, HTTPStatus.MOVED_PERMANENTLY) |
| + location = response.getheader('Location') |
| + self.assertFalse(location.startswith('//'), msg=location) |
| + self.assertEqual(location, expected_location, |
| + msg='Expected Location header to start with a single / and ' |
| + 'end with a / as this is a directory redirect.') |
| + |
| + # ///python.org... triple-slash prefix, no trailing slash |
| + attack3_url = f'//{url}' |
| + response = self.request(attack3_url) |
| + self.check_status_and_reason(response, HTTPStatus.MOVED_PERMANENTLY) |
| + self.assertEqual(response.getheader('Location'), expected_location) |
| + |
| + # If the second word in the http request (Request-URI for the http |
| + # method) is a full URI, we don't worry about it, as that'll be parsed |
| + # and reassembled as a full URI within BaseHTTPRequestHandler.send_head |
| + # so no errant scheme-less //netloc//evil.co/ domain mixup can happen. |
| + attack_scheme_netloc_2slash_url = f'https://pypi.org/{url}' |
| + expected_scheme_netloc_location = f'{attack_scheme_netloc_2slash_url}/' |
| + response = self.request(attack_scheme_netloc_2slash_url) |
| + self.check_status_and_reason(response, HTTPStatus.MOVED_PERMANENTLY) |
| + location = response.getheader('Location') |
| + # We're just ensuring that the scheme and domain make it through, if |
| + # there are or aren't multiple slashes at the start of the path that |
| + # follows that isn't important in this Location: header. |
| + self.assertTrue(location.startswith('https://pypi.org/'), msg=location) |
| + |
| def test_get(self): |
| #constructs the path relative to the root directory of the HTTPServer |
| response = self.request(self.base_url + '/test') |
| diff --git a/Misc/NEWS.d/next/Security/2022-06-15-20-09-23.gh-issue-87389.QVaC3f.rst b/Misc/NEWS.d/next/Security/2022-06-15-20-09-23.gh-issue-87389.QVaC3f.rst |
| new file mode 100644 |
| index 000000000000..029d437190de |
| --- /dev/null |
| +++ b/Misc/NEWS.d/next/Security/2022-06-15-20-09-23.gh-issue-87389.QVaC3f.rst |
| @@ -0,0 +1,3 @@ |
| +:mod:`http.server`: Fix an open redirection vulnerability in the HTTP server |
| +when an URI path starts with ``//``. Vulnerability discovered, and initial |
| +fix proposed, by Hamza Avvan. |