Made is_safe_url() reject URLs that start with control characters.

This is a security fix; disclosure to follow shortly.

docs/releases/1.4.20.txt

@@ -5,3 +5,22 @@ Django 1.4.20 release notes
 *March 18, 2015*
 
 Django 1.4.20 fixes one security issue in 1.4.19.
+
+Mitigated possible XSS attack via user-supplied redirect URLs
+=============================================================
+
+Django relies on user input in some cases (e.g.
+:func:`django.contrib.auth.views.login` and :doc:`i18n </topics/i18n/index>`)
+to redirect the user to an "on success" URL. The security checks for these
+redirects (namely ``django.utils.http.is_safe_url()``) accepted URLs with
+leading control characters and so considered URLs like ``\x08javascript:...``
+safe. This issue doesn't affect Django currently, since we only put this URL
+into the ``Location`` response header and browsers seem to ignore JavaScript
+there. Browsers we tested also treat URLs prefixed with control characters such
+as ``%08//example.com`` as relative paths so redirection to an unsafe target
+isn't a problem either.
+
+However, 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 as some browsers such as Google Chrome ignore control
+characters at the start of a URL in an anchor ``href``.

docs/releases/1.6.11.txt

@@ -22,3 +22,22 @@ it detects the length of the string it's processing increases. Remember that
 absolutely NO guarantee is provided about the results of ``strip_tags()`` being
 HTML safe. So NEVER mark safe the result of a ``strip_tags()`` call without
 escaping it first, for example with :func:`~django.utils.html.escape`.
+
+Mitigated possible XSS attack via user-supplied redirect URLs
+=============================================================
+
+Django relies on user input in some cases (e.g.
+:func:`django.contrib.auth.views.login` and :doc:`i18n </topics/i18n/index>`)
+to redirect the user to an "on success" URL. The security checks for these
+redirects (namely ``django.utils.http.is_safe_url()``) accepted URLs with
+leading control characters and so considered URLs like ``\x08javascript:...``
+safe. This issue doesn't affect Django currently, since we only put this URL
+into the ``Location`` response header and browsers seem to ignore JavaScript
+there. Browsers we tested also treat URLs prefixed with control characters such
+as ``%08//example.com`` as relative paths so redirection to an unsafe target
+isn't a problem either.
+
+However, 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 as some browsers such as Google Chrome ignore control
+characters at the start of a URL in an anchor ``href``.

docs/releases/1.7.7.txt

@@ -23,6 +23,25 @@ absolutely NO guarantee is provided about the results of ``strip_tags()`` being
 HTML safe. So NEVER mark safe the result of a ``strip_tags()`` call without
 escaping it first, for example with :func:`~django.utils.html.escape`.
 
+Mitigated possible XSS attack via user-supplied redirect URLs
+=============================================================
+
+Django relies on user input in some cases (e.g.
+:func:`django.contrib.auth.views.login` and :doc:`i18n </topics/i18n/index>`)
+to redirect the user to an "on success" URL. The security checks for these
+redirects (namely ``django.utils.http.is_safe_url()``) accepted URLs with
+leading control characters and so considered URLs like ``\x08javascript:...``
+safe. This issue doesn't affect Django currently, since we only put this URL
+into the ``Location`` response header and browsers seem to ignore JavaScript
+there. Browsers we tested also treat URLs prefixed with control characters such
+as ``%08//example.com`` as relative paths so redirection to an unsafe target
+isn't a problem either.
+
+However, 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 as some browsers such as Google Chrome ignore control
+characters at the start of a URL in an anchor ``href``.
+
 Bugfixes
 ========