Issue: Cross-site scripting (XSS) in admin interface

The Django administrative application, django.contrib.admin, provides functionality for CRUD (Creation, Retrieval, Updating and Deleting) operations by trusted users, including facilities for both automatic and customized data-manipulation interfaces.

When displaying the value of a URLField -- a model field type for storing URLs -- this interface treated the values of such fields as safe, thus failing to properly accommodate the potential for dangerous values. A proof-of-concept application has been provided to the Django project, showing how this can be exploited to perform XSS in the administrative interface.

In a normal Django deployment, this will only affect the administrative interface, as the incorrect handling occurs only in form-widget code in django.contrib.admin. It is, however, possible that other applications may be affected, if those applications make use of form widgets provided by the admin interface.

To remedy this issue, the widget in question -- django.contrib.admin.widgets.AdminURLFieldWidget -- has been corrected to treat its value the same as any other potentially-user-supplied value; in other words, it will be treated as unsafe, and subject to Django's (enabled by default) output escaping.

Thanks to Łukasz Langa for reporting this issue to us.

Issue: Possible XSS via is_safe_url

A common pattern in Django applications is for a view to accept, via querystring parameter, a URL to redirect to upon successful completion of the view's processing. This pattern is used in code bundled with Django itself; for example, the login view in django.contrib.auth.views, which accepts such a parameter to determine where to send a user following successful login.

A utility function -- django.utils.http.is_safe_url() -- is provided and used to validate that this URL is on the current host (either via fully-qualified or relative URL), so as to avoid potentially dangerous redirects from maliciously-constructed querystrings.

The is_safe_url() function works as intended for HTTP and HTTPS URLs, but due to the manner in which it parses the URL, will permit redirects to other schemes, such as javascript:. While the Django project is unaware of any demonstrated ability to perform cross-site scripting attacks via this mechanism, the potential for such is sufficient to trigger a security response.

To remedy this issue, the is_safe_url() function has been modified to properly recognize and reject URLs which specify a scheme other than HTTP or HTTPS.

Thanks to Nick Bruun for reporting this issue to us.

Affected versions

The URLField XSS issue affects the following versions of Django:

• Django 1.5
• Django 1.6 (currently at beta status)
• Django master development branch

The is_safe_url() issue affects the following versions of Django:

• Django 1.4
• Django 1.5
• Django 1.6 (currently at beta status)
• Django master development branch

Resolution

Patches have been applied to Django's master development branch, and to the 1.6, 1.5 and 1.4 release branches, which resolve the issues described above. The patches may be obtained directly from the following changesets:

On the development master branch:

• master is_safe_url patch
• master URLField patch

On the Django 1.6 release branch:

• 1.6 is_safe_url patch
• 1.6 URLField patch

On the Django 1.5 release branch:

• 1.5 is_safe_url patch
• 1.5 URLField patch

On the Django 1.4 release branch:

• 1.4 is_safe_url patch

The following new releases have been issued:

• Django 1.6 beta 2 (download Django 1.6b2 | 1.6b2 checksums)
• Django 1.5.2 (download Django 1.5.2 | 1.5.2 checksums)
• Django 1.4.6 (download Django 1.4.6 | 1.4.6 checksums)

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.