8000 [1.8.x] Made is_safe_url() reject URLs that start with control charac… · django/django@770427c · GitHub
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[1.8.x] Made is_safe_url() reject URLs that start with control characters.
This is a security fix; disclosure to follow shortly.
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-2
lines changed

5 files changed

+68
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‎django/utils/http.py‎

Lines changed: 8 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -5,6 +5,7 @@
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import datetime
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import re
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import sys
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import unicodedata
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from binascii import Error as BinasciiError
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from email.utils import formatdate
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@@ -272,9 +273,10 @@ def is_safe_url(url, host=None):
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Always returns ``False`` on an empty url.
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"""
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if url is not None:
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url = url.strip()
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if not url:
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return False
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url = url.strip()
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# Chrome treats \ completely as /
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url = url.replace('\\', '/')
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# Chrome considers any URL with more than two slashes to be absolute, but
@@ -288,5 +290,10 @@ def is_safe_url(url, host=None):
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# allow this syntax.
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if not url_info.netloc and url_info.scheme:
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return False
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# Forbid URLs that start with control characters. Some browsers (like
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# Chrome) ignore quite a few control characters at the start of a
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# URL and might consider the URL as scheme relative.
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if unicodedata.category(url[0])[0] == 'C':
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return False
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return ((not url_info.netloc or url_info.netloc == host) and
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(not url_info.scheme or url_info.scheme in ['http', 'https']))

‎docs/releases/1.4.20.txt‎

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Original file line numberDiff line numberDiff line change
@@ -5,3 +5,22 @@ Django 1.4.20 release notes
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*March 18, 2015*
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Django 1.4.20 fixes one security issue in 1.4.19.
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Mitigated possible XSS attack via user-supplied redirect URLs
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=============================================================
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Django relies on user input in some cases (e.g.
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:func:`django.contrib.auth.views.login` and :doc:`i18n </topics/i18n/index>`)
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to redirect the user to an "on success" URL. The security checks for these
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redirects (namely ``django.utils.http.is_safe_url()``) accepted URLs with
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leading control characters and so considered URLs like ``\x08javascript:...``
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safe. This issue doesn't affect Django currently, since we only put this URL
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into the ``Location`` response header and browsers seem to ignore JavaScript
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there. Browsers we tested also treat URLs prefixed with control characters such
20+
as ``%08//example.com`` as relative paths so redirection to an unsafe target
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isn't a problem either.
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However, if a developer relies on ``is_safe_url()`` to
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provide safe redirect targets and puts such a URL into a link, they could
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suffer from an XSS attack as some browsers such as Google Chrome ignore control
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characters at the start of a URL in an anchor ``href``.

‎docs/releases/1.6.11.txt‎

Lines changed: 19 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -22,3 +22,22 @@ it detects the length of the string it's processing increases. Remember that
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absolutely NO guarantee is provided about the results of ``strip_tags()`` being
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HTML safe. So NEVER mark safe the result of a ``strip_tags()`` call without
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escaping it first, for example with :func:`~django.utils.html.escape`.
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Mitigated possible XSS attack via user-supplied redirect URLs
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=============================================================
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Django relies on user input in some cases (e.g.
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:func:`django.contrib.auth.views.login` and :doc:`i18n </topics/i18n/index>`)
31+
to redirect the user to an "on success" URL. The security checks for these
32+
redirects (namely ``django.utils.http.is_safe_url()``) accepted URLs with
33+
leading control characters and so considered URLs like ``\x08javascript:...``
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safe. This issue doesn't affect Django currently, since we only put this URL
35+
into the ``Location`` response header and browsers seem to ignore JavaScript
36+
there. Browsers we tested also treat URLs prefixed with control characters such
37+
as ``%08//example.com`` as relative paths so redirection to an unsafe target
38+
isn't a problem either.
39+
40+
However, if a developer relies on ``is_safe_url()`` to
41+
provide safe redirect targets and puts such a URL into a link, they could
42+
suffer from an XSS attack as some browsers such as Google Chrome ignore control
43+
characters at the start of a URL in an anchor ``href``.

‎docs/releases/1.7.7.txt‎

Lines changed: 19 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -23,6 +23,25 @@ absolutely NO guarantee is provided about the results of ``strip_tags()`` being
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HTML safe. So NEVER mark safe the result of a ``strip_tags()`` call without
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escaping it first, for example with :func:`~django.utils.html.escape`.
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Mitigated possible XSS attack via user-supplied redirect URLs
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=============================================================
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Django relies on user input in some cases (e.g.
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:func:`django.contrib.auth.views.login` and :doc:`i18n </topics/i18n/index>`)
31+
to redirect the user to an "on success" URL. The security checks for these
32+
redirects (namely ``django.utils.http.is_safe_url()``) accepted URLs with
33+
leading control characters and so considered URLs like ``\x08javascript:...``
34+
safe. This issue doesn't affect Django currently, since we only put this URL
35+
into the ``Location`` response header and browsers seem to ignore JavaScript
36+
there. Browsers we tested also treat URLs prefixed with control characters such
37+
as ``%08//example.com`` as relative paths so redirection to an unsafe target
38+
isn't a problem either.
39+
40+
However, if a developer relies on ``is_safe_url()`` to
41+
provide safe redirect targets and puts such a URL into a link, they could
42+
suffer from an XSS attack as some browsers such as Google Chrome ignore control
43+
characters at the start of a URL in an anchor ``href``.
44+
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Bugfixes
2746
========
2847

‎tests/utils_tests/test_http.py‎

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -115,7 +115,9 @@ def test_is_safe_url(self):
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'http:\/example.com',
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'http:/\example.com',
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'javascript:alert("XSS")',
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'\njavascript:alert(x)'):
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'\njavascript:alert(x)',
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'\x08//example.com',
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'\n'):
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self.assertFalse(http.is_safe_url(bad_url, host='testserver'), "%s should be blocked" % bad_url)
120122
for good_url in ('/view/?param=http://example.com',
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'/view/?param=https://example.com',

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