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gh-87389: Fix an open redirection vulnerability in http.server. (GH-9… · python/cpython@defaa2b · GitHub
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gh-87389: Fix an open redirection vulnerability in http.server. (GH-93879) (GH-94093)
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 4abab6b) Co-authored-by: Gregory P. Smith <greg@krypto.org>
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‎Lib/http/server.py‎

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@@ -330,6 +330,13 @@ def parse_request(self):
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return False
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self.command, self.path = command, path
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# gh-87389: The purpose of replacing '//' with '/' is to protect
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# against open redirect attacks possibly triggered if the path starts
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# with '//' because http clients treat //path as an absolute URI
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# without scheme (similar to http://path) rather than a path.
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if self.path.startswith('//'):
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self.path = '/' + self.path.lstrip('/') # Reduce to a single /
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# Examine the headers and look for a Connection directive.
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try:
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self.headers = http.client.parse_headers(self.rfile,

‎Lib/test/test_httpservers.py‎

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@@ -331,7 +331,7 @@ class request_handler(NoLogRequestHandler, SimpleHTTPRequestHandler):
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pass
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def setUp(self):
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BaseTestCase.setUp(self)
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super().setUp()
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self.cwd = os.getcwd()
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basetempdir = tempfile.gettempdir()
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os.chdir(basetempdir)
@@ -359,7 +359,7 @@ def tearDown(self):
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except:
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pass
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finally:
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BaseTestCase.tearDown(self)
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super().tearDown()
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def check_status_and_reason(self, response, status, data=None):
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def close_conn():
@@ -415,6 +415,55 @@ def test_undecodable_filename(self):
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self.check_status_and_reason(response, HTTPStatus.OK,
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data=support.TESTFN_UNDECODABLE)
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def test_get_dir_redirect_location_domain_injection_bug(self):
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"""Ensure //evil.co/..%2f../../X does not put //evil.co/ in Location.
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//netloc/ in a Location header is a redirect to a new host.
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https://github.com/python/cpython/issues/87389
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This checks that a path resolving to a directory on our server cannot
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resolve into a redirect to another server.
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"""
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os.mkdir(os.path.join(self.tempdir, 'existing_directory'))
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url = f'/python.org/..%2f..%2f..%2f..%2f..%2f../%0a%0d/../{self.tempdir_name}/existing_directory'
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expected_location = f'{url}/' # /python.org.../ single slash single prefix, trailing slash
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# Canonicalizes to /tmp/tempdir_name/existing_directory which does
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# exist and is a dir, triggering the 301 redirect logic.
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response = self.request(url)
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self.check_status_and_reason(response, HTTPStatus.MOVED_PERMANENTLY)
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location = response.getheader('Location')
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self.assertEqual(location, expected_location, msg='non-attack failed!')
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# //python.org... multi-slash prefix, no trailing slash
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attack_url = f'/{url}'
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response = self.request(attack_url)
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self.check_status_and_reason(response, HTTPStatus.MOVED_PERMANENTLY)
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location = response.getheader('Location')
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self.assertFalse(location.startswith('//'), msg=location)
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self.assertEqual(location, expected_location,
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msg='Expected Location header to start with a single / and '
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'end with a / as this is a directory redirect.')
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# ///python.org... triple-slash prefix, no trailing slash
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attack3_url = f'//{url}'
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response = self.request(attack3_url)
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self.check_status_and_reason(response, HTTPStatus.MOVED_PERMANENTLY)
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self.assertEqual(response.getheader('Location'), expected_location)
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# If the second word in the http request (Request-URI for the http
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# method) is a full URI, we don't worry about it, as that'll be parsed
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# and reassembled as a full URI within BaseHTTPRequestHandler.send_head
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# so no errant scheme-less //netloc//evil.co/ domain mixup can happen.
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attack_scheme_netloc_2slash_url = f'https://pypi.org/{url}'
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expected_scheme_netloc_location = f'{attack_scheme_netloc_2slash_url}/'
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response = self.request(attack_scheme_netloc_2slash_url)
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self.check_status_and_reason(response, HTTPStatus.MOVED_PERMANENTLY)
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location = response.getheader('Location')
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# We're just ensuring that the scheme and domain make it through, if
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# there are or aren't multiple slashes at the start of the path that
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# follows that isn't important in this Location: header.
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self.assertTrue(location.startswith('https://pypi.org/'), msg=location)
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def test_get(self):
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#constructs the path relative to the root directory of the HTTPServer
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response = self.request(self.base_url + '/test')

‎Misc/NEWS.d/next/Security/2022-06-15-20-09-23.gh-issue-87389.QVaC3f.rst‎

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:mod:`http.server`: Fix an open redirection vulnerability in the HTTP server
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when an URI path starts with ``//``. Vulnerability discovered, and initial
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fix proposed, by Hamza Avvan.

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