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Ensure that passwords are never long enough for a DoS. 

* Limit the password length to 4096 bytes
  * Password hashers will raise a ValueError
  * django.contrib.auth forms will fail validation
* Document in release notes that this is a backwards incompatible change

Thanks to Josh Wright for the report, and Donald Stufft for the patch.

This is a security fix; disclosure to follow shortly.
This commit is contained in:
Russell Keith-Magee 2013-09-15 13:40:16 +08:00
parent 351a061497
commit aae5a96d57
4 changed files with 153 additions and 17 deletions
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48
django/contrib/auth/forms.py
View File

@ -14,7 +14,9 @@ from django.utils.translation import ugettext, ugettext_lazy as _
from django.contrib.auth import authenticate, get_user_model
from django.contrib.auth.models import User
from django.contrib.auth.hashers import UNUSABLE_PASSWORD_PREFIX, identify_hasher
from django.contrib.auth.hashers import (
MAXIMUM_PASSWORD_LENGTH, UNUSABLE_PASSWORD_PREFIX, identify_hasher,
)
from django.contrib.auth.tokens import default_token_generator
from django.contrib.sites.models import get_current_site
@ -80,9 +82,10 @@ class UserCreationForm(forms.ModelForm):
'invalid': _("This value may contain only letters, numbers and "
"@/./+/-/_ characters.")})
password1 = forms.CharField(label=_("Password"),
widget=forms.PasswordInput)
widget=forms.PasswordInput, max_length=MAXIMUM_PASSWORD_LENGTH)
password2 = forms.CharField(label=_("Password confirmation"),
widget=forms.PasswordInput,
max_length=MAXIMUM_PASSWORD_LENGTH,
help_text=_("Enter the same password as above, for verification."))
class Meta:
@ -156,7 +159,11 @@ class AuthenticationForm(forms.Form):
username/password logins.
"""
username = forms.CharField(max_length=254)
password = forms.CharField(label=_("Password"), widget=forms.PasswordInput)
password = forms.CharField(
label=_("Password"),
widget=forms.PasswordInput,
max_length=MAXIMUM_PASSWORD_LENGTH,
)
error_messages = {
'invalid_login': _("Please enter a correct %(username)s and password. "
@ -279,10 +286,16 @@ class SetPasswordForm(forms.Form):
error_messages = {
'password_mismatch': _("The two password fields didn't match."),
}
new_password1 = forms.CharField(label=_("New password"),
widget=forms.PasswordInput)
new_password2 = forms.CharField(label=_("New password confirmation"),
widget=forms.PasswordInput)
new_password1 = forms.CharField(
label=_("New password"),
widget=forms.PasswordInput,
max_length=MAXIMUM_PASSWORD_LENGTH,
)
new_password2 = forms.CharField(
label=_("New password confirmation"),
widget=forms.PasswordInput,
max_length=MAXIMUM_PASSWORD_LENGTH,
)
def __init__(self, user, *args, **kwargs):
self.user = user
@ -315,8 +328,11 @@ class PasswordChangeForm(SetPasswordForm):
'password_incorrect': _("Your old password was entered incorrectly. "
"Please enter it again."),
})
old_password = forms.CharField(label=_("Old password"),
widget=forms.PasswordInput)
old_password = forms.CharField(
label=_("Old password"),
widget=forms.PasswordInput,
max_length=MAXIMUM_PASSWORD_LENGTH,
)
def clean_old_password(self):
"""
@ -343,10 +359,16 @@ class AdminPasswordChangeForm(forms.Form):
error_messages = {
'password_mismatch': _("The two password fields didn't match."),
}
password1 = forms.CharField(label=_("Password"),
widget=forms.PasswordInput)
password2 = forms.CharField(label=_("Password (again)"),
widget=forms.PasswordInput)
password1 = forms.CharField(
label=_("Password"),
widget=forms.PasswordInput,
max_length=MAXIMUM_PASSWORD_LENGTH,
)
password2 = forms.CharField(
label=_("Password (again)"),
widget=forms.PasswordInput,
max_length=MAXIMUM_PASSWORD_LENGTH,
)
def __init__(self, user, *args, **kwargs):
self.user = user

29
django/contrib/auth/hashers.py
View File

@ -3,6 +3,7 @@ from __future__ import unicode_literals
import base64
import binascii
from collections import OrderedDict
import functools
import hashlib
import importlib
@ -19,6 +20,7 @@ from django.utils.translation import ugettext_noop as _
UNUSABLE_PASSWORD_PREFIX = '!' # This will never be a valid encoded hash
UNUSABLE_PASSWORD_SUFFIX_LENGTH = 40 # number of random chars to add after UNUSABLE_PASSWORD_PREFIX
MAXIMUM_PASSWORD_LENGTH = 4096 # The maximum length a password can be to prevent DoS
HASHERS = None # lazily loaded from PASSWORD_HASHERS
PREFERRED_HASHER = None # defaults to first item in PASSWORD_HASHERS
@ -31,6 +33,18 @@ def reset_hashers(**kwargs):
PREFERRED_HASHER = None
def password_max_length(max_length):
def inner(fn):
@functools.wraps(fn)
def wrapper(self, password, *args, **kwargs):
if len(password) > max_length:
raise ValueError("Invalid password; Must be less than or equal"
" to %d bytes" % max_length)
return fn(self, password, *args, **kwargs)
return wrapper
return inner
def is_password_usable(encoded):
if encoded is None or encoded.startswith(UNUSABLE_PASSWORD_PREFIX):
return False
@ -225,6 +239,7 @@ class PBKDF2PasswordHasher(BasePasswordHasher):
iterations = 10000
digest = hashlib.sha256
@password_max_length(MAXIMUM_PASSWORD_LENGTH)
def encode(self, password, salt, iterations=None):
assert password is not None
assert salt and '$' not in salt
@ -234,6 +249,7 @@ class PBKDF2PasswordHasher(BasePasswordHasher):
hash = base64.b64encode(hash).decode('ascii').strip()
return "%s$%d$%s$%s" % (self.algorithm, iterations, salt, hash)
@password_max_length(MAXIMUM_PASSWORD_LENGTH)
def verify(self, password, encoded):
algorithm, iterations, salt, hash = encoded.split('$', 3)
assert algorithm == self.algorithm
@ -280,6 +296,7 @@ class BCryptSHA256PasswordHasher(BasePasswordHasher):
bcrypt = self._load_library()
return bcrypt.gensalt(self.rounds)
@password_max_length(MAXIMUM_PASSWORD_LENGTH)
def encode(self, password, salt):
bcrypt = self._load_library()
# Need to reevaluate the force_bytes call once bcrypt is supported on
@ -297,6 +314,7 @@ class BCryptSHA256PasswordHasher(BasePasswordHasher):
data = bcrypt.hashpw(password, salt)
return "%s$%s" % (self.algorithm, force_text(data))
@password_max_length(MAXIMUM_PASSWORD_LENGTH)
def verify(self, password, encoded):
algorithm, data = encoded.split('$', 1)
assert algorithm == self.algorithm
@ -353,12 +371,14 @@ class SHA1PasswordHasher(BasePasswordHasher):
"""
algorithm = "sha1"
@password_max_length(MAXIMUM_PASSWORD_LENGTH)
def encode(self, password, salt):
assert password is not None
assert salt and '$' not in salt
hash = hashlib.sha1(force_bytes(salt + password)).hexdigest()
return "%s$%s$%s" % (self.algorithm, salt, hash)
@password_max_length(MAXIMUM_PASSWORD_LENGTH)
def verify(self, password, encoded):
algorithm, salt, hash = encoded.split('$', 2)
assert algorithm == self.algorithm
@ -381,12 +401,14 @@ class MD5PasswordHasher(BasePasswordHasher):
"""
algorithm = "md5"
@password_max_length(MAXIMUM_PASSWORD_LENGTH)
def encode(self, password, salt):
assert password is not None
assert salt and '$' not in salt
hash = hashlib.md5(force_bytes(salt + password)).hexdigest()
return "%s$%s$%s" % (self.algorithm, salt, hash)
@password_max_length(MAXIMUM_PASSWORD_LENGTH)
def verify(self, password, encoded):
algorithm, salt, hash = encoded.split('$', 2)
assert algorithm == self.algorithm
@ -417,11 +439,13 @@ class UnsaltedSHA1PasswordHasher(BasePasswordHasher):
def salt(self):
return ''
@password_max_length(MAXIMUM_PASSWORD_LENGTH)
def encode(self, password, salt):
assert salt == ''
hash = hashlib.sha1(force_bytes(password)).hexdigest()
return 'sha1$$%s' % hash
@password_max_length(MAXIMUM_PASSWORD_LENGTH)
def verify(self, password, encoded):
encoded_2 = self.encode(password, '')
return constant_time_compare(encoded, encoded_2)
@ -451,10 +475,12 @@ class UnsaltedMD5PasswordHasher(BasePasswordHasher):
def salt(self):
return ''
@password_max_length(MAXIMUM_PASSWORD_LENGTH)
def encode(self, password, salt):
assert salt == ''
return hashlib.md5(force_bytes(password)).hexdigest()
@password_max_length(MAXIMUM_PASSWORD_LENGTH)
def verify(self, password, encoded):
if len(encoded) == 37 and encoded.startswith('md5$$'):
encoded = encoded[5:]
@ -480,6 +506,7 @@ class CryptPasswordHasher(BasePasswordHasher):
def salt(self):
return get_random_string(2)
@password_max_length(MAXIMUM_PASSWORD_LENGTH)
def encode(self, password, salt):
crypt = self._load_library()
assert len(salt) == 2
@ -487,6 +514,7 @@ class CryptPasswordHasher(BasePasswordHasher):
# we don't need to store the salt, but Django used to do this
return "%s$%s$%s" % (self.algorithm, '', data)
@password_max_length(MAXIMUM_PASSWORD_LENGTH)
def verify(self, password, encoded):
crypt = self._load_library()
algorithm, salt, data = encoded.split('$', 2)
@ -501,4 +529,3 @@ class CryptPasswordHasher(BasePasswordHasher):
(_('salt'), salt),
(_('hash'), mask_hash(data, show=3)),
])

85
django/contrib/auth/tests/test_hashers.py
View File

@ -5,9 +5,12 @@ import unittest
from unittest import skipUnless
from django.conf.global_settings import PASSWORD_HASHERS as default_hashers
from django.contrib.auth.hashers import (is_password_usable, BasePasswordHasher,
check_password, make_password, PBKDF2PasswordHasher, load_hashers, PBKDF2SHA1PasswordHasher,
get_hasher, identify_hasher, UNUSABLE_PASSWORD_PREFIX, UNUSABLE_PASSWORD_SUFFIX_LENGTH)
from django.contrib.auth.hashers import (
is_password_usable, BasePasswordHasher, check_password, make_password,
PBKDF2PasswordHasher, load_hashers, PBKDF2SHA1PasswordHasher, get_hasher,
identify_hasher, UNUSABLE_PASSWORD_PREFIX, UNUSABLE_PASSWORD_SUFFIX_LENGTH,
MAXIMUM_PASSWORD_LENGTH, password_max_length
)
from django.utils import six
@ -39,6 +42,12 @@ class TestUtilsHashPass(unittest.TestCase):
self.assertTrue(is_password_usable(blank_encoded))
self.assertTrue(check_password('', blank_encoded))
self.assertFalse(check_password(' ', blank_encoded))
# Long password
self.assertRaises(
ValueError,
make_password,
b"1" * (MAXIMUM_PASSWORD_LENGTH + 1),
)
def test_pkbdf2(self):
encoded = make_password('lètmein', 'seasalt', 'pbkdf2_sha256')
@ -54,6 +63,14 @@ class TestUtilsHashPass(unittest.TestCase):
self.assertTrue(is_password_usable(blank_encoded))
self.assertTrue(check_password('', blank_encoded))
self.assertFalse(check_password(' ', blank_encoded))
# Long password
self.assertRaises(
ValueError,
make_password,
b"1" * (MAXIMUM_PASSWORD_LENGTH + 1),
"seasalt",
"pbkdf2_sha256",
)
def test_sha1(self):
encoded = make_password('lètmein', 'seasalt', 'sha1')
@ -69,6 +86,14 @@ class TestUtilsHashPass(unittest.TestCase):
self.assertTrue(is_password_usable(blank_encoded))
self.assertTrue(check_password('', blank_encoded))
self.assertFalse(check_password(' ', blank_encoded))
# Long password
self.assertRaises(
ValueError,
make_password,
b"1" * (MAXIMUM_PASSWORD_LENGTH + 1),
"seasalt",
"sha1",
)
def test_md5(self):
encoded = make_password('lètmein', 'seasalt', 'md5')
@ -84,6 +109,14 @@ class TestUtilsHashPass(unittest.TestCase):
self.assertTrue(is_password_usable(blank_encoded))
self.assertTrue(check_password('', blank_encoded))
self.assertFalse(check_password(' ', blank_encoded))
# Long password
self.assertRaises(
ValueError,
make_password,
b"1" * (MAXIMUM_PASSWORD_LENGTH + 1),
"seasalt",
"md5",
)
def test_unsalted_md5(self):
encoded = make_password('lètmein', '', 'unsalted_md5')
@ -102,6 +135,14 @@ class TestUtilsHashPass(unittest.TestCase):
self.assertTrue(is_password_usable(blank_encoded))
self.assertTrue(check_password('', blank_encoded))
self.assertFalse(check_password(' ', blank_encoded))
# Long password
self.assertRaises(
ValueError,
make_password,
b"1" * (MAXIMUM_PASSWORD_LENGTH + 1),
"",
"unsalted_md5",
)
def test_unsalted_sha1(self):
encoded = make_password('lètmein', '', 'unsalted_sha1')
@ -119,6 +160,14 @@ class TestUtilsHashPass(unittest.TestCase):
self.assertTrue(is_password_usable(blank_encoded))
self.assertTrue(check_password('', blank_encoded))
self.assertFalse(check_password(' ', blank_encoded))
# Long password
self.assertRaises(
ValueError,
make_password,
b"1" * (MAXIMUM_PASSWORD_LENGTH + 1),
"",
"unslated_sha1",
)
@skipUnless(crypt, "no crypt module to generate password.")
def test_crypt(self):
@ -134,6 +183,14 @@ class TestUtilsHashPass(unittest.TestCase):
self.assertTrue(is_password_usable(blank_encoded))
self.assertTrue(check_password('', blank_encoded))
self.assertFalse(check_password(' ', blank_encoded))
# Long password
self.assertRaises(
ValueError,
make_password,
b"1" * (MAXIMUM_PASSWORD_LENGTH + 1),
"seasalt",
"crypt",
)
@skipUnless(bcrypt, "bcrypt not installed")
def test_bcrypt_sha256(self):
@ -156,6 +213,13 @@ class TestUtilsHashPass(unittest.TestCase):
self.assertTrue(is_password_usable(blank_encoded))
self.assertTrue(check_password('', blank_encoded))
self.assertFalse(check_password(' ', blank_encoded))
# Long password
self.assertRaises(
ValueError,
make_password,
b"1" * (MAXIMUM_PASSWORD_LENGTH + 1),
hasher="bcrypt_sha256",
)
@skipUnless(bcrypt, "bcrypt not installed")
def test_bcrypt(self):
@ -171,6 +235,13 @@ class TestUtilsHashPass(unittest.TestCase):
self.assertTrue(is_password_usable(blank_encoded))
self.assertTrue(check_password('', blank_encoded))
self.assertFalse(check_password(' ', blank_encoded))
# Long password
self.assertRaises(
ValueError,
make_password,
b"1" * (MAXIMUM_PASSWORD_LENGTH + 1),
hasher="bcrypt",
)
def test_unusable(self):
encoded = make_password(None)
@ -203,6 +274,14 @@ class TestUtilsHashPass(unittest.TestCase):
self.assertFalse(is_password_usable('lètmein_badencoded'))
self.assertFalse(is_password_usable(''))
def test_max_password_length_decorator(self):
@password_max_length(10)
def encode(s, password, salt):
return True
self.assertTrue(encode(None, b"1234", b"1234"))
self.assertRaises(ValueError, encode, None, b"1234567890A", b"1234")
def test_low_level_pkbdf2(self):
hasher = PBKDF2PasswordHasher()
encoded = hasher.encode('lètmein', 'seasalt')

8
docs/releases/1.7.txt
View File

@ -402,6 +402,14 @@ Miscellaneous
Rationale behind this is removal of dependency of non-contrib code on
contrib applications.
* Passwords longer than 4096 bytes in length will no longer work and will
instead raise a ``ValueError`` when using the hasher directory or the
built in forms shipped with ``django.contrib.auth`` will fail validation.
The rationale behind this is a possibility of a Denial of Service attack when
using a slow password hasher, such as the default PBKDF2, and sending very
large passwords.
Features deprecated in 1.7
==========================