[3.2.x] Fixed #32713, Fixed CVE-2021-32052 -- Prevented newlines and tabs from being accepted in URLValidator on Python 3.9.5+.

In Python 3.9.5+ urllib.parse() automatically removes ASCII newlines
and tabs from URLs [1, 2]. Unfortunately it created an issue in
the URLValidator. URLValidator uses urllib.urlsplit() and
urllib.urlunsplit() for creating a URL variant with Punycode which no
longer contains newlines and tabs in Python 3.9.5+. As a consequence,
the regular expression matched the URL (without unsafe characters) and
the source value (with unsafe characters) was considered valid.

[1] https://bugs.python.org/issue43882 and
[2] https://github.com/python/cpython/commit/76cd81d60310d65d01f9d7b48a8985d8ab89c8b4

Backport of e1e81aa1c4427411e3c68facdd761229ffea6f6f from main.

1 files changed, 22 insertions, 0 deletions

diff --git a/docs/releases/3.1.10.txt b/docs/releases/3.1.10.txt
new file mode 100644
index 0000000000..e9a8fcc2d8
--- /dev/null
+++ b/docs/releases/3.1.10.txt
@@ -0,0 +1,22 @@
+===========================
+Django 3.1.10 release notes
+===========================
+
+*May 6, 2021*
+
+Django 3.1.10 fixes a security issue in 3.1.9.
+
+CVE-2021-32052: Header injection possibility since ``URLValidator`` accepted newlines in input on Python 3.9.5+
+===============================================================================================================
+
+On Python 3.9.5+, :class:`~django.core.validators.URLValidator` didn't prohibit
+newlines and tabs. If you used values with newlines in HTTP response, you could
+suffer from header injection attacks. Django itself wasn't vulnerable because
+:class:`~django.http.HttpResponse` prohibits newlines in HTTP headers.
+
+Moreover, the ``URLField`` form field which uses ``URLValidator`` silently
+removes newlines and tabs on Python 3.9.5+, so the possibility of newlines
+entering your data only existed if you are using this validator outside of the
+form fields.
+
+This issue was introduced by the :bpo:`43882` fix.