diff --git a/django/utils/html.py b/django/utils/html.py index 9f9fbdb2a5a..1cf131b8a09 100644 --- a/django/utils/html.py +++ b/django/utils/html.py @@ -175,8 +175,10 @@ def strip_tags(value): # is redundant, but helps to reduce number of executions of _strip_once. while '<' in value and '>' in value: new_value = _strip_once(value) - if new_value == value: - # _strip_once was not able to detect more tags + if len(new_value) >= len(value): + # _strip_once was not able to detect more tags or length increased + # due to http://bugs.python.org/issue20288 + # (affects Python 2 < 2.7.7 and Python 3 < 3.3.5) break value = new_value return value diff --git a/docs/releases/1.6.11.txt b/docs/releases/1.6.11.txt index da10a44301d..a7d020c004e 100644 --- a/docs/releases/1.6.11.txt +++ b/docs/releases/1.6.11.txt @@ -5,3 +5,20 @@ 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 :func:`~django.utils.html.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 :func:`~django.utils.html.escape`. diff --git a/docs/releases/1.7.7.txt b/docs/releases/1.7.7.txt index 86079fd70d5..c8c7aa9ee5c 100644 --- a/docs/releases/1.7.7.txt +++ b/docs/releases/1.7.7.txt @@ -6,6 +6,23 @@ Django 1.7.7 release notes Django 1.7.7 fixes several bugs and security issues in 1.7.6. +Denial-of-service possibility with ``strip_tags()`` +=================================================== + +Last year :func:`~django.utils.html.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 :func:`~django.utils.html.escape`. + Bugfixes ======== diff --git a/tests/utils_tests/test_html.py b/tests/utils_tests/test_html.py index db490466828..7456b67d502 100644 --- a/tests/utils_tests/test_html.py +++ b/tests/utils_tests/test_html.py @@ -82,6 +82,9 @@ class TestUtilsHtml(TestCase): ('a

b

c', 'abc'), ('de

f', 'def'), ('foobar', 'foobar'), + # caused infinite loop on Pythons not patched with + # http://bugs.python.org/issue20288 + ('&gotcha&#;<>', '&gotcha&#;<>'), ) for value, output in items: self.check_output(f, value, output)