From ee5def757d914f51facc0ae8cd2b0ff2f03c300e Mon Sep 17 00:00:00 2001 From: Pascal Wittmann Date: Tue, 7 Jun 2022 10:11:03 +0200 Subject: [PATCH] gh-79096: Protect cookie file created by {LWP,Mozilla}CookieJar.save() (GH-93463) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Note: This change is not effective on Microsoft Windows. Cookies can store sensitive information and should therefore be protected against unauthorized third parties. This is also described in issue #79096. The filesystem permissions are currently set to 644, everyone can read the file. This commit changes the permissions to 600, only the creater of the file can read and modify it. This improves security, because it reduces the attack surface. Now the attacker needs control of the user that created the cookie or a ways to circumvent the filesystems permissions. This change is backwards incompatible. Systems that rely on world-readable cookies will breake. However, one could argue that those are misconfigured in the first place. (backported to 3.9 by Michał Górny) --- Lib/http/cookiejar.py | 4 +-- Lib/test/test_http_cookiejar.py | 31 +++++++++++++++++++ ...2-06-03-12-52-53.gh-issue-79096.YVoxgC.rst | 1 + 3 files changed, 34 insertions(+), 2 deletions(-) create mode 100644 Misc/NEWS.d/next/Security/2022-06-03-12-52-53.gh-issue-79096.YVoxgC.rst diff --git a/Lib/http/cookiejar.py b/Lib/http/cookiejar.py index 47ed5c3d64ab7d..a2c66aa5ffad8b 100644 --- a/Lib/http/cookiejar.py +++ b/Lib/http/cookiejar.py @@ -1887,7 +1887,7 @@ def save(self, filename=None, ignore_discard=False, ignore_expires=False): if self.filename is not None: filename = self.filename else: raise ValueError(MISSING_FILENAME_TEXT) - with open(filename, "w") as f: + with os.fdopen(os.open(filename, os.O_CREAT | os.O_WRONLY, 0o600), 'w') as f: # There really isn't an LWP Cookies 2.0 format, but this indicates # that there is extra information in here (domain_dot and # port_spec) while still being compatible with libwww-perl, I hope. @@ -2082,7 +2082,7 @@ def save(self, filename=None, ignore_discard=False, ignore_expires=False): if self.filename is not None: filename = self.filename else: raise ValueError(MISSING_FILENAME_TEXT) - with open(filename, "w") as f: + with os.fdopen(os.open(filename, os.O_CREAT | os.O_WRONLY, 0o600), 'w') as f: f.write(self.header) now = time.time() for cookie in self: diff --git a/Lib/test/test_http_cookiejar.py b/Lib/test/test_http_cookiejar.py index 83945509d71482..99e57f7d05a3b4 100644 --- a/Lib/test/test_http_cookiejar.py +++ b/Lib/test/test_http_cookiejar.py @@ -1,6 +1,7 @@ """Tests for http/cookiejar.py.""" import os +import sys import re import test.support import time @@ -15,6 +16,7 @@ reach, is_HDN, domain_match, user_domain_match, request_path, request_port, request_host) +mswindows = (sys.platform == "win32") class DateTimeTests(unittest.TestCase): @@ -366,6 +368,35 @@ def test_lwp_valueless_cookie(self): except OSError: pass self.assertEqual(c._cookies["www.acme.com"]["/"]["boo"].value, None) + @unittest.skipIf(mswindows, "windows file permissions are incompatible with file modes") + def test_lwp_filepermissions(self): + # Cookie file should only be readable by the creator + filename = test.support.TESTFN + c = LWPCookieJar() + interact_netscape(c, "http://www.acme.com/", 'boo') + try: + c.save(filename, ignore_discard=True) + status = os.stat(filename) + print(status.st_mode) + self.assertEqual(oct(status.st_mode)[-3:], '600') + finally: + try: os.unlink(filename) + except OSError: pass + + @unittest.skipIf(mswindows, "windows file permissions are incompatible with file modes") + def test_mozilla_filepermissions(self): + # Cookie file should only be readable by the creator + filename = test.support.TESTFN + c = MozillaCookieJar() + interact_netscape(c, "http://www.acme.com/", 'boo') + try: + c.save(filename, ignore_discard=True) + status = os.stat(filename) + self.assertEqual(oct(status.st_mode)[-3:], '600') + finally: + try: os.unlink(filename) + except OSError: pass + def test_bad_magic(self): # OSErrors (eg. file doesn't exist) are allowed to propagate filename = test.support.TESTFN diff --git a/Misc/NEWS.d/next/Security/2022-06-03-12-52-53.gh-issue-79096.YVoxgC.rst b/Misc/NEWS.d/next/Security/2022-06-03-12-52-53.gh-issue-79096.YVoxgC.rst new file mode 100644 index 00000000000000..9ec3335dc71b92 --- /dev/null +++ b/Misc/NEWS.d/next/Security/2022-06-03-12-52-53.gh-issue-79096.YVoxgC.rst @@ -0,0 +1 @@ +LWPCookieJar and MozillaCookieJar create files with file mode 600 instead of 644 (Microsoft Windows is not affected)