blob: e16b99bcb96a7e24a24fc663d4aa057ebd8db0e6 [file] [log] [blame]
From 0b297d4ff1c0e4480ad33acae793fbaf4bf015b4 Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@python.org>
Date: Thu, 2 Apr 2020 02:52:20 +0200
Subject: [PATCH] bpo-39503: CVE-2020-8492: Fix AbstractBasicAuthHandler
(GH-18284)
Upstream-Status: Backport
(https://github.com/python/cpython/commit/0b297d4ff1c0e4480ad33acae793fbaf4bf015b4)
CVE: CVE-2020-8492
The AbstractBasicAuthHandler class of the urllib.request module uses
an inefficient regular expression which can be exploited by an
attacker to cause a denial of service. Fix the regex to prevent the
catastrophic backtracking. Vulnerability reported by Ben Caller
and Matt Schwager.
AbstractBasicAuthHandler of urllib.request now parses all
WWW-Authenticate HTTP headers and accepts multiple challenges per
header: use the realm of the first Basic challenge.
Co-Authored-By: Serhiy Storchaka <storchaka@gmail.com>
Signed-off-by: Trevor Gamblin <trevor.gamblin@windriver.com>
---
Lib/test/test_urllib2.py | 90 ++++++++++++-------
Lib/urllib/request.py | 69 ++++++++++----
.../2020-03-25-16-02-16.bpo-39503.YmMbYn.rst | 3 +
.../2020-01-30-16-15-29.bpo-39503.B299Yq.rst | 5 ++
4 files changed, 115 insertions(+), 52 deletions(-)
create mode 100644 Misc/NEWS.d/next/Library/2020-03-25-16-02-16.bpo-39503.YmMbYn.rst
create mode 100644 Misc/NEWS.d/next/Security/2020-01-30-16-15-29.bpo-39503.B299Yq.rst
diff --git a/Lib/test/test_urllib2.py b/Lib/test/test_urllib2.py
index 8abedaac98..e69ac3e213 100644
--- a/Lib/test/test_urllib2.py
+++ b/Lib/test/test_urllib2.py
@@ -1446,40 +1446,64 @@ class HandlerTests(unittest.TestCase):
bypass = {'exclude_simple': True, 'exceptions': []}
self.assertTrue(_proxy_bypass_macosx_sysconf('test', bypass))
- def test_basic_auth(self, quote_char='"'):
- opener = OpenerDirector()
- password_manager = MockPasswordManager()
- auth_handler = urllib.request.HTTPBasicAuthHandler(password_manager)
- realm = "ACME Widget Store"
- http_handler = MockHTTPHandler(
- 401, 'WWW-Authenticate: Basic realm=%s%s%s\r\n\r\n' %
- (quote_char, realm, quote_char))
- opener.add_handler(auth_handler)
- opener.add_handler(http_handler)
- self._test_basic_auth(opener, auth_handler, "Authorization",
- realm, http_handler, password_manager,
- "http://acme.example.com/protected",
- "http://acme.example.com/protected",
- )
-
- def test_basic_auth_with_single_quoted_realm(self):
- self.test_basic_auth(quote_char="'")
-
- def test_basic_auth_with_unquoted_realm(self):
- opener = OpenerDirector()
- password_manager = MockPasswordManager()
- auth_handler = urllib.request.HTTPBasicAuthHandler(password_manager)
- realm = "ACME Widget Store"
- http_handler = MockHTTPHandler(
- 401, 'WWW-Authenticate: Basic realm=%s\r\n\r\n' % realm)
- opener.add_handler(auth_handler)
- opener.add_handler(http_handler)
- with self.assertWarns(UserWarning):
+ def check_basic_auth(self, headers, realm):
+ with self.subTest(realm=realm, headers=headers):
+ opener = OpenerDirector()
+ password_manager = MockPasswordManager()
+ auth_handler = urllib.request.HTTPBasicAuthHandler(password_manager)
+ body = '\r\n'.join(headers) + '\r\n\r\n'
+ http_handler = MockHTTPHandler(401, body)
+ opener.add_handler(auth_handler)
+ opener.add_handler(http_handler)
self._test_basic_auth(opener, auth_handler, "Authorization",
- realm, http_handler, password_manager,
- "http://acme.example.com/protected",
- "http://acme.example.com/protected",
- )
+ realm, http_handler, password_manager,
+ "http://acme.example.com/protected",
+ "http://acme.example.com/protected")
+
+ def test_basic_auth(self):
+ realm = "realm2@example.com"
+ realm2 = "realm2@example.com"
+ basic = f'Basic realm="{realm}"'
+ basic2 = f'Basic realm="{realm2}"'
+ other_no_realm = 'Otherscheme xxx'
+ digest = (f'Digest realm="{realm2}", '
+ f'qop="auth, auth-int", '
+ f'nonce="dcd98b7102dd2f0e8b11d0f600bfb0c093", '
+ f'opaque="5ccc069c403ebaf9f0171e9517f40e41"')
+ for realm_str in (
+ # test "quote" and 'quote'
+ f'Basic realm="{realm}"',
+ f"Basic realm='{realm}'",
+
+ # charset is ignored
+ f'Basic realm="{realm}", charset="UTF-8"',
+
+ # Multiple challenges per header
+ f'{basic}, {basic2}',
+ f'{basic}, {other_no_realm}',
+ f'{other_no_realm}, {basic}',
+ f'{basic}, {digest}',
+ f'{digest}, {basic}',
+ ):
+ headers = [f'WWW-Authenticate: {realm_str}']
+ self.check_basic_auth(headers, realm)
+
+ # no quote: expect a warning
+ with support.check_warnings(("Basic Auth Realm was unquoted",
+ UserWarning)):
+ headers = [f'WWW-Authenticate: Basic realm={realm}']
+ self.check_basic_auth(headers, realm)
+
+ # Multiple headers: one challenge per header.
+ # Use the first Basic realm.
+ for challenges in (
+ [basic, basic2],
+ [basic, digest],
+ [digest, basic],
+ ):
+ headers = [f'WWW-Authenticate: {challenge}'
+ for challenge in challenges]
+ self.check_basic_auth(headers, realm)
def test_proxy_basic_auth(self):
opener = OpenerDirector()
diff --git a/Lib/urllib/request.py b/Lib/urllib/request.py
index 7fe50535da..2a3d71554f 100644
--- a/Lib/urllib/request.py
+++ b/Lib/urllib/request.py
@@ -937,8 +937,15 @@ class AbstractBasicAuthHandler:
# allow for double- and single-quoted realm values
# (single quotes are a violation of the RFC, but appear in the wild)
- rx = re.compile('(?:.*,)*[ \t]*([^ \t]+)[ \t]+'
- 'realm=(["\']?)([^"\']*)\\2', re.I)
+ rx = re.compile('(?:^|,)' # start of the string or ','
+ '[ \t]*' # optional whitespaces
+ '([^ \t]+)' # scheme like "Basic"
+ '[ \t]+' # mandatory whitespaces
+ # realm=xxx
+ # realm='xxx'
+ # realm="xxx"
+ 'realm=(["\']?)([^"\']*)\\2',
+ re.I)
# XXX could pre-emptively send auth info already accepted (RFC 2617,
# end of section 2, and section 1.2 immediately after "credentials"
@@ -950,27 +957,51 @@ class AbstractBasicAuthHandler:
self.passwd = password_mgr
self.add_password = self.passwd.add_password
+ def _parse_realm(self, header):
+ # parse WWW-Authenticate header: accept multiple challenges per header
+ found_challenge = False
+ for mo in AbstractBasicAuthHandler.rx.finditer(header):
+ scheme, quote, realm = mo.groups()
+ if quote not in ['"', "'"]:
+ warnings.warn("Basic Auth Realm was unquoted",
+ UserWarning, 3)
+
+ yield (scheme, realm)
+
+ found_challenge = True
+
+ if not found_challenge:
+ if header:
+ scheme = header.split()[0]
+ else:
+ scheme = ''
+ yield (scheme, None)
+
def http_error_auth_reqed(self, authreq, host, req, headers):
# host may be an authority (without userinfo) or a URL with an
# authority
- # XXX could be multiple headers
- authreq = headers.get(authreq, None)
+ headers = headers.get_all(authreq)
+ if not headers:
+ # no header found
+ return
- if authreq:
- scheme = authreq.split()[0]
- if scheme.lower() != 'basic':
- raise ValueError("AbstractBasicAuthHandler does not"
- " support the following scheme: '%s'" %
- scheme)
- else:
- mo = AbstractBasicAuthHandler.rx.search(authreq)
- if mo:
- scheme, quote, realm = mo.groups()
- if quote not in ['"',"'"]:
- warnings.warn("Basic Auth Realm was unquoted",
- UserWarning, 2)
- if scheme.lower() == 'basic':
- return self.retry_http_basic_auth(host, req, realm)
+ unsupported = None
+ for header in headers:
+ for scheme, realm in self._parse_realm(header):
+ if scheme.lower() != 'basic':
+ unsupported = scheme
+ continue
+
+ if realm is not None:
+ # Use the first matching Basic challenge.
+ # Ignore following challenges even if they use the Basic
+ # scheme.
+ return self.retry_http_basic_auth(host, req, realm)
+
+ if unsupported is not None:
+ raise ValueError("AbstractBasicAuthHandler does not "
+ "support the following scheme: %r"
+ % (scheme,))
def retry_http_basic_auth(self, host, req, realm):
user, pw = self.passwd.find_user_password(realm, host)
diff --git a/Misc/NEWS.d/next/Library/2020-03-25-16-02-16.bpo-39503.YmMbYn.rst b/Misc/NEWS.d/next/Library/2020-03-25-16-02-16.bpo-39503.YmMbYn.rst
new file mode 100644
index 0000000000..be80ce79d9
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-03-25-16-02-16.bpo-39503.YmMbYn.rst
@@ -0,0 +1,3 @@
+:class:`~urllib.request.AbstractBasicAuthHandler` of :mod:`urllib.request`
+now parses all WWW-Authenticate HTTP headers and accepts multiple challenges
+per header: use the realm of the first Basic challenge.
diff --git a/Misc/NEWS.d/next/Security/2020-01-30-16-15-29.bpo-39503.B299Yq.rst b/Misc/NEWS.d/next/Security/2020-01-30-16-15-29.bpo-39503.B299Yq.rst
new file mode 100644
index 0000000000..9f2800581c
--- /dev/null
+++ b/Misc/NEWS.d/next/Security/2020-01-30-16-15-29.bpo-39503.B299Yq.rst
@@ -0,0 +1,5 @@
+CVE-2020-8492: The :class:`~urllib.request.AbstractBasicAuthHandler` class of the
+:mod:`urllib.request` module uses an inefficient regular expression which can
+be exploited by an attacker to cause a denial of service. Fix the regex to
+prevent the catastrophic backtracking. Vulnerability reported by Ben Caller
+and Matt Schwager.
--
2.24.1