commit 5f1757142febd95994caa1c0f64c1a0c161982c3
Author: Mariusz Felisiak <felisiak.mariusz@gmail.com>
Date:   Wed Jul 10 20:30:12 2024 +0200

    Fixed CVE-2024-41991 -- Prevented potential ReDoS in django.utils.html.urlize() and AdminURLFieldWidget.
    
    Thanks Seokchan Yoon for the report.
    
    Co-authored-by: Sarah Boyce <42296566+sarahboyce@users.noreply.github.com>

diff --git a/django/contrib/admin/widgets.py b/django/contrib/admin/widgets.py
index aeb74773a..b7dd0d87a 100644
--- a/django/contrib/admin/widgets.py
+++ b/django/contrib/admin/widgets.py
@@ -339,7 +339,7 @@ class AdminURLFieldWidget(forms.URLInput):
         context = super().get_context(name, value, attrs)
         context['current_label'] = _('Currently:')
         context['change_label'] = _('Change:')
-        context['widget']['href'] = smart_urlquote(context['widget']['value']) if value else ''
+        context['widget']['href'] = smart_urlquote(context['widget']['value']) if url_valid else ''
         context['url_valid'] = url_valid
         return context
 
diff --git a/django/utils/html.py b/django/utils/html.py
index 1123e38f6c..154c820d34 100644
--- a/django/utils/html.py
+++ b/django/utils/html.py
@@ -28,7 +28,7 @@ simple_url_2_re = _lazy_re_compile(
     r'^www\.|^(?!http)\w[^@]+\.(com|edu|gov|int|mil|net|org)($|/.*)$',
     re.IGNORECASE
 )
-
+MAX_URL_LENGTH = 2048
 
 @keep_lazy(str, SafeString)
 def escape(text):
@@ -298,6 +298,10 @@ def urlize(text, trim_url_limit=None, nofollow=False, autoescape=False):
         except ValueError:
             # value contains more than one @.
             return False
+        # Max length for domain name labels is 63 characters per RFC 1034.
+        # Helps to avoid ReDoS vectors in the domain part.
+        if len(p2) > 63:
+            return False
         # Dot must be in p2 (e.g. example.com)
         if '.' not in p2 or p2.startswith('.'):
             return False
@@ -316,9 +322,9 @@ def urlize(text, trim_url_limit=None, nofollow=False, autoescape=False):
             # Make URL we want to point to.
             url = None
             nofollow_attr = ' rel="nofollow"' if nofollow else ''
-            if simple_url_re.match(middle):
+            if len(middle) <= MAX_URL_LENGTH and simple_url_re.match(middle):
                 url = smart_urlquote(html.unescape(middle))
-            elif simple_url_2_re.match(middle):
+            elif len(middle) <= MAX_URL_LENGTH and simple_url_2_re.match(middle):
                 url = smart_urlquote('http://%s' % html.unescape(middle))
             elif ':' not in middle and is_email_simple(middle):
                 local, domain = middle.rsplit('@', 1)
diff --git a/tests/admin_widgets/tests.py b/tests/admin_widgets/tests.py
index 517e060b80..5da4adf8c9 100644
--- a/tests/admin_widgets/tests.py
+++ b/tests/admin_widgets/tests.py
@@ -353,7 +353,12 @@ class AdminSplitDateTimeWidgetTest(SimpleTestCase):
 class AdminURLWidgetTest(SimpleTestCase):
     def test_get_context_validates_url(self):
         w = widgets.AdminURLFieldWidget()
-        for invalid in ['', '/not/a/full/url/', 'javascript:alert("Danger XSS!")']:
+        for invalid in [
+            "",
+            "/not/a/full/url/",
+            'javascript:alert("Danger XSS!")',
+            "http://" + "한.글." * 1_000_000 + "com",
+        ]:
             with self.subTest(url=invalid):
                 self.assertFalse(w.get_context('name', invalid, {})['url_valid'])
         self.assertTrue(w.get_context('name', 'http://example.com', {})['url_valid'])
diff --git a/tests/utils_tests/test_html.py b/tests/utils_tests/test_html.py
index 30f5ba68e..93458acd1 100644
--- a/tests/utils_tests/test_html.py
+++ b/tests/utils_tests/test_html.py
@@ -255,6 +255,15 @@ class TestUtilsHtml(SimpleTestCase):
                 'Search for <a href="http://google.com/?q=">google.com/?q=</a>!'
             ),
             ('foo@example.com', '<a href="mailto:foo@example.com">foo@example.com</a>'),
+            (
+                "test@" + "한.글." * 15 + "aaa",
+                '<a href="mailto:test@'
+                + "xn--6q8b.xn--bj0b." * 15
+                + 'aaa">'
+                + "test@"
+                + "한.글." * 15
+                + "aaa</a>",
+            ),
         )
         for value, output in tests:
             with self.subTest(value=value):
@@ -263,6 +272,10 @@ class TestUtilsHtml(SimpleTestCase):
     def test_urlize_unchanged_inputs(self):
         tests = (
             ('a' + '@a' * 50000) + 'a',  # simple_email_re catastrophic test
+            # Unicode domain catastrophic tests.
+            "a@" + "한.글." * 1_000_000 + "a",
+            "http://" + "한.글." * 1_000_000 + "com",
+            "www." + "한.글." * 1_000_000 + "com",
             ('a' + '.' * 1000000) + 'a',  # trailing_punctuation catastrophic test
             'foo@',
             '@foo.com',