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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.
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commit aae5a96d5754ad34e48b7f673ef2411a3bbc1015 1 parent 351a061
@freakboy3742 freakboy3742 authored
View
48 django/contrib/auth/forms.py
@@ -14,7 +14,9 @@
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
View
29 django/contrib/auth/hashers.py
@@ -3,6 +3,7 @@
import base64
import binascii
from collections import OrderedDict
+import functools
import hashlib
import importlib
@@ -19,6 +20,7 @@
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 '$' not in salt
@@ -234,6 +249,7 @@ def encode(self, password, salt, iterations=None):
hash = base64.b64encode(hash).decode('ascii').strip()
return "%s$%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('$', 3)
assert algorithm == self.algorithm
@@ -280,6 +296,7 @@ def salt(self):
bcrypt = self._load_library()
return bcrypt.gensalt(self.rounds)
+ @password_max_length(MAXIMUM_PASSWORD_LENGTH)
def encode(self, password, salt):
bcrypt = self._load_library()
# Need to reevaluate the force_bytes call once bcrypt is supported on
@@ -297,6 +314,7 @@ def encode(self, password, salt):
data = bcrypt.hashpw(password, salt)
return "%s$%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 @@ def encode(self, password, salt):
# 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 @@ def safe_summary(self, encoded):
(_('salt'), salt),
(_('hash'), mask_hash(data, show=3)),
])
-
View
85 django/contrib/auth/tests/test_hashers.py
@@ -5,9 +5,12 @@
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 @@ def test_simple(self):
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 @@ def test_pkbdf2(self):
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 @@ def test_sha1(self):
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 @@ def test_md5(self):
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 @@ def test_unsalted_md5(self):
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 @@ def test_unsalted_sha1(self):
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 @@ def test_crypt(self):
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 @@ def test_bcrypt_sha256(self):
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 @@ def test_bcrypt(self):
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 @@ def test_bad_encoded(self):
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')
View
8 docs/releases/1.7.txt
@@ -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
==========================
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