Commit 5ecc0f82 authored by Russell Keith-Magee's avatar Russell Keith-Magee
Browse files

[1.6.x] 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.

Backport of aae5a96d from master.
parent 4c4954a3

django/contrib/auth/forms.py

+35 −13
Original line number Diff line number Diff line
@@ -15,7 +15,9 @@ 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
@@ -81,9 +83,10 @@ 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:
@@ -157,7 +160,11 @@ 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. "
@@ -264,10 +271,16 @@ 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
@@ -300,8 +313,11 @@ 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):

        """
@@ -328,10 +344,16 @@ 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

django/contrib/auth/hashers.py

+28 −1
Original line number Diff line number Diff line
@@ -2,6 +2,7 @@ from __future__ import unicode_literals 


import base64

import binascii

import functools

import hashlib



from django.dispatch import receiver
@@ -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)),

        ])

django/contrib/auth/tests/test_hashers.py

+82 −3
Original line number Diff line number Diff line
@@ -2,9 +2,12 @@ 
from __future__ import unicode_literals



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

from django.utils import unittest

from django.utils.unittest import skipUnless
@@ -38,6 +41,12 @@ 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')
@@ -53,6 +62,14 @@ 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')
@@ -68,6 +85,14 @@ 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')
@@ -83,6 +108,14 @@ 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')
@@ -101,6 +134,14 @@ 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')
@@ -118,6 +159,14 @@ 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):
@@ -133,6 +182,14 @@ 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):
@@ -155,6 +212,13 @@ 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):
@@ -170,6 +234,13 @@ 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)
@@ -202,6 +273,14 @@ 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')

docs/releases/1.6.txt

+8 −0
Original line number Diff line number Diff line
@@ -869,6 +869,14 @@ Miscellaneous 
  to prevent django from deleting the temporary .pot file it generates before

  creating the .po file.



* 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 1.6

==========================