[1.8.x] Fixed CVE-2016-2513 -- Fixed user enumeration timing attack during login.

This is a security fix.

1 files changed, 33 insertions, 0 deletions

diff --git a/docs/releases/1.8.10.txt b/docs/releases/1.8.10.txt
index 73c7cc04a4..d57afc470d 100644
--- a/docs/releases/1.8.10.txt
+++ b/docs/releases/1.8.10.txt
@@ -22,6 +22,39 @@ redirecting to this URL sends the user to ``attacker.com``.
 Also, if a developer relies on ``is_safe_url()`` to provide safe redirect
 targets and puts such a URL into a link, they could suffer from an XSS attack.
 
+CVE-2016-2513: User enumeration through timing difference on password hasher work factor upgrade
+================================================================================================
+
+In each major version of Django since 1.6, the default number of iterations for
+the ``PBKDF2PasswordHasher`` and its subclasses has increased. This improves
+the security of the password as the speed of hardware increases, however, it
+also creates a timing difference between a login request for a user with a
+password encoded in an older number of iterations and login request for a
+nonexistent user (which runs the default hasher's default number of iterations
+since Django 1.6).
+
+This only affects users who haven't logged in since the iterations were
+increased. The first time a user logs in after an iterations increase, their
+password is updated with the new iterations and there is no longer a timing
+difference.
+
+The new ``BasePasswordHasher.harden_runtime()`` method allows hashers to bridge
+the runtime gap between the work factor (e.g. iterations) supplied in existing
+encoded passwords and the default work factor of the hasher. This method
+is implemented for ``PBKDF2PasswordHasher``  and ``BCryptPasswordHasher``.
+The number of rounds for the latter hasher hasn't changed since Django 1.4, but
+some projects may subclass it and increase the work factor as needed.
+
+A warning will be emitted for any :ref:`third-party password hashers that don't
+implement <write-your-own-password-hasher>` a ``harden_runtime()`` method.
+
+If you have different password hashes in your database (such as SHA1 hashes
+from users who haven't logged in since the default hasher switched to PBKDF2
+in Django 1.4), the timing difference on a login request for these users may be
+even greater and this fix doesn't remedy that difference (or any difference
+when changing hashers). You may be able to :ref:`upgrade those hashes
+<wrapping-password-hashers>` to prevent a timing attack for that case.
+
 Bugfixes
 ========