From 2273e65e11dd0234f2f51ebaef61fc6e848d4059 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Micha=C5=82=20G=C3=B3rny?= Date: Thu, 10 Sep 2020 13:35:39 +0200 Subject: [PATCH 02/24] bpo-39503: CVE-2020-8492: Fix AbstractBasicAuthHandler (GH-18284) (GH-19304) 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 (cherry picked from commit 0b297d4ff1c0e4480ad33acae793fbaf4bf015b4) [rebased for py2.7] --- Lib/test/test_urllib2.py | 81 ++++++++++++++++++++++++++-------------- Lib/urllib2.py | 60 +++++++++++++++++++++++------ 2 files changed, 101 insertions(+), 40 deletions(-) diff --git a/Lib/test/test_urllib2.py b/Lib/test/test_urllib2.py index 20a0f58143..0adbb13c43 100644 --- a/Lib/test/test_urllib2.py +++ b/Lib/test/test_urllib2.py @@ -1128,42 +1128,67 @@ class HandlerTests(unittest.TestCase): self.assertEqual(req.get_host(), "proxy.example.com:3128") self.assertEqual(req.get_header("Proxy-authorization"),"FooBar") - def test_basic_auth(self, quote_char='"'): + def check_basic_auth(self, headers, realm): opener = OpenerDirector() password_manager = MockPasswordManager() auth_handler = urllib2.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) ) + 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" - ) - - 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 = urllib2.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) - msg = "Basic Auth Realm was unquoted" - with test_support.check_warnings((msg, UserWarning)): - self._test_basic_auth(opener, auth_handler, "Authorization", - realm, http_handler, password_manager, - "http://acme.example.com/protected", - "http://acme.example.com/protected" - ) - + "http://acme.example.com/protected") + + def test_basic_auth(self): + realm = "realm2@example.com" + realm2 = "realm2@example.com" + basic = 'Basic realm="{realm}"'.format(realm=realm) + basic2 = 'Basic realm="{realm2}"'.format(realm2=realm2) + other_no_realm = 'Otherscheme xxx' + digest = ('Digest realm="{realm2}", ' + 'qop="auth, auth-int", ' + 'nonce="dcd98b7102dd2f0e8b11d0f600bfb0c093", ' + 'opaque="5ccc069c403ebaf9f0171e9517f40e41"' + .format(realm2=realm2)) + for realm_str in ( + # test "quote" and 'quote' + 'Basic realm="{realm}"'.format(realm=realm), + "Basic realm='{realm}'".format(realm=realm), + + # charset is ignored + 'Basic realm="{realm}", charset="UTF-8"'.format(realm=realm), + + # Multiple challenges per header + ', '.join((basic, basic2)), + ', '.join((basic, other_no_realm)), + ', '.join((other_no_realm, basic)), + ', '.join((basic, digest)), + ', '.join((digest, basic)), + ): + headers = ['WWW-Authenticate: {realm_str}' + .format(realm_str=realm_str)] + self.check_basic_auth(headers, realm) + + # no quote: expect a warning + with test_support.check_warnings(("Basic Auth Realm was unquoted", + UserWarning)): + headers = ['WWW-Authenticate: Basic realm={realm}' + .format(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 = ['WWW-Authenticate: {challenge}' + .format(challenge=challenge) + for challenge in challenges] + self.check_basic_auth(headers, realm) def test_proxy_basic_auth(self): opener = OpenerDirector() diff --git a/Lib/urllib2.py b/Lib/urllib2.py index 8b634ada37..b2d1fad6f2 100644 --- a/Lib/urllib2.py +++ b/Lib/urllib2.py @@ -856,8 +856,15 @@ 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" @@ -869,23 +876,52 @@ 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.getheaders(authreq) + if not headers: + # no header found + return - if authreq: - 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': + 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) if pw is not None: -- 2.30.1