| 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 |
| |