# Django 2.1.8.dev20190330215650 documentation

# Django 1.6.11 release notes

March 18, 2015

Django 1.6.11 fixes two security issues in 1.6.10.

## Denial-of-service possibility with `strip_tags()`

Last year `strip_tags()` was changed to work iteratively. The problem is that the size of the input it's processing can increase on each iteration which results in an infinite loop in `strip_tags()`. This issue only affects versions of Python that haven't received a bugfix in HTMLParser; namely Python < 2.7.7 and 3.3.5. Some operating system vendors have also backported the fix for the Python bug into their packages of earlier versions.

To remedy this issue, `strip_tags()` will now return the original input if 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 `escape()`.

## Mitigated possible XSS attack via user-supplied redirect URLs

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 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`.