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):
('ab
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)