Django Weblog: Django security releases issued: 1.9.3 and 1.8.10

CVE-2016-2512: Malicious redirect and possible XSS attack via user-supplied redirect URLs containing basic auth

Django relies on user input in some cases (e.g. django.contrib.auth.views.login() and i18n) to redirect the user to an "on success" URL. The security check for these redirects (namely django.utils.http.is_safe_url()) considered some URLs with basic authentication credentials "safe" when they shouldn't be.

For example, a URL like http://mysite.example.com\@attacker.com would be considered safe if the request's host is http://mysite.example.com, but 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.

Thanks Mark Striemer for reporting the issue.

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 third-party password hashers that don't implement 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 upgrade those hashes to prevent a timing attack for that case.

Thanks Sjoerd Job Postmus for reporting the issue.

Affected supported versions

• Django master development branch
• Django 1.9
• Django 1.8

Per our supported versions policy, Django 1.7 and older are no longer receiving security updates.

Resolution

Patches to resolve the issues have been applied to Django's master development branch and the 1.9 and 1.8 release branches. The patches may be obtained from the following changesets:

On the development master branch: * is_safe_url() patch * hashers patch

On the 1.9 release branch: * is_safe_url() patch * hashers patch

On the 1.8 release branch: * is_safe_url() patch * hashers patch

The following new releases has been issued:

• Django 1.9.3 (download Django 1.9.3 | 1.9.3 checksums)
• Django 1.8.10 (download Django 1.8.10 | 1.8.10 checksums)

The PGP key ID used for these releases is Tim Graham: 1E8ABDC773EDE252.

General notes regarding security reporting

As always, we ask that potential security issues be reported via private email to security@djangoproject.com, and not via Django's Trac instance or the django-developers list. Please see our security policies for further information.