From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
<31488909+miss-islington@users.noreply.github.com>
Date: Wed, 22 Jun 2022 15:05:00 -0700
Subject: [PATCH] 00386: CVE-2021-28861
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)
Upstream: https://github.com/python/cpython/pull/93879
Tracking bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2120642
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 60a4dadf03..ce05be13d3 100644
--- a/Lib/http/server.py
+++ b/Lib/http/server.py
@@ -323,6 +323,13 @@ class BaseHTTPRequestHandler(socketserver.StreamRequestHandler):
return False
self.command, self.path, self.request_version = command, path, version
+ # 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 66e937e04b..5a0a7c3f74 100644
--- a/Lib/test/test_httpservers.py
+++ b/Lib/test/test_httpservers.py
@@ -324,7 +324,7 @@ class SimpleHTTPServerTestCase(BaseTestCase):
pass
def setUp(self):
- BaseTestCase.setUp(self)
+ super().setUp()
self.cwd = os.getcwd()
basetempdir = tempfile.gettempdir()
os.chdir(basetempdir)
@@ -343,7 +343,7 @@ class SimpleHTTPServerTestCase(BaseTestCase):
except:
pass
finally:
- BaseTestCase.tearDown(self)
+ super().tearDown()
def check_status_and_reason(self, response, status, data=None):
def close_conn():
@@ -399,6 +399,55 @@ class SimpleHTTPServerTestCase(BaseTestCase):
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 0000000000..029d437190
--- /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.