Fixed CVE-2023-36053 -- Prevented potential ReDoS in EmailValidator and URLValidator.

Thanks Seokchan Yoon for reports.

django/core/validators.py

@@ -104,6 +104,7 @@ class URLValidator(RegexValidator):
     message = _("Enter a valid URL.")
     schemes = ["http", "https", "ftp", "ftps"]
     unsafe_chars = frozenset("\t\r\n")
+    max_length = 2048
 
     def __init__(self, schemes=None, **kwargs):
         super().__init__(**kwargs)
@@ -111,7 +112,7 @@ class URLValidator(RegexValidator):
             self.schemes = schemes
 
     def __call__(self, value):
-        if not isinstance(value, str):
+        if not isinstance(value, str) or len(value) > self.max_length:
             raise ValidationError(self.message, code=self.code, params={"value": value})
         if self.unsafe_chars.intersection(value):
             raise ValidationError(self.message, code=self.code, params={"value": value})
@@ -203,7 +204,9 @@ class EmailValidator:
             self.domain_allowlist = allowlist
 
     def __call__(self, value):
-        if not value or "@" not in value:
+        # The maximum length of an email is 320 characters per RFC 3696
+        # section 3.
+        if not value or "@" not in value or len(value) > 320:
             raise ValidationError(self.message, code=self.code, params={"value": value})
 
         user_part, domain_part = value.rsplit("@", 1)

django/forms/fields.py

@@ -616,6 +616,9 @@ class EmailField(CharField):
     default_validators = [validators.validate_email]
 
     def __init__(self, **kwargs):
+        # The default maximum length of an email is 320 characters per RFC 3696
+        # section 3.
+        kwargs.setdefault("max_length", 320)
         super().__init__(strip=True, **kwargs)
 
 

docs/ref/forms/fields.txt

@@ -596,7 +596,12 @@ For each field, we describe the default widget used if you don't specify
     * Error message keys: ``required``, ``invalid``
 
     Has the optional arguments ``max_length``, ``min_length``, and
-    ``empty_value`` which work just as they do for :class:`CharField`.
+    ``empty_value`` which work just as they do for :class:`CharField`. The
+    ``max_length`` argument defaults to 320 (see :rfc:`3696#section-3`).
+
+    .. versionchanged:: 3.2.20
+
+        The default value for ``max_length`` was changed to 320 characters.
 
 ``FileField``
 -------------

docs/ref/validators.txt

@@ -133,6 +133,11 @@ to, or in lieu of custom ``field.clean()`` methods.
     :param code: If not ``None``, overrides :attr:`code`.
     :param allowlist: If not ``None``, overrides :attr:`allowlist`.
 
+    An :class:`EmailValidator` ensures that a value looks like an email, and
+    raises a :exc:`~django.core.exceptions.ValidationError` with
+    :attr:`message` and :attr:`code` if it doesn't. Values longer than 320
+    characters are always considered invalid.
+
     .. attribute:: message
 
         The error message used by
@@ -154,13 +159,19 @@ to, or in lieu of custom ``field.clean()`` methods.
         validation, so you'd need to add them to the ``allowlist`` as
         necessary.
 
+    .. versionchanged:: 3.2.20
+
+        In older versions, values longer than 320 characters could be
+        considered valid.
+
 ``URLValidator``
 ----------------
 
 .. class:: URLValidator(schemes=None, regex=None, message=None, code=None)
 
     A :class:`RegexValidator` subclass that ensures a value looks like a URL,
-    and raises an error code of ``'invalid'`` if it doesn't.
+    and raises an error code of ``'invalid'`` if it doesn't. Values longer than
+    :attr:`max_length` characters are always considered invalid.
 
     Loopback addresses and reserved IP spaces are considered valid. Literal
     IPv6 addresses (:rfc:`3986#section-3.2.2`) and Unicode domains are both
@@ -177,6 +188,18 @@ to, or in lieu of custom ``field.clean()`` methods.
 
         .. _valid URI schemes: https://www.iana.org/assignments/uri-schemes/uri-schemes.xhtml
 
+    .. attribute:: max_length
+
+        .. versionadded:: 3.2.20
+
+        The maximum length of values that could be considered valid. Defaults
+        to 2048 characters.
+
+    .. versionchanged:: 3.2.20
+
+        In older versions, values longer than 2048 characters could be
+        considered valid.
+
 ``validate_email``
 ------------------
 

docs/releases/3.2.20.txt

@@ -6,4 +6,9 @@ Django 3.2.20 release notes
 
 Django 3.2.20 fixes a security issue with severity "moderate" in 3.2.19.
 
-...
+CVE-2023-36053: Potential regular expression denial of service vulnerability in ``EmailValidator``/``URLValidator``
+===================================================================================================================
+
+``EmailValidator`` and ``URLValidator`` were subject to potential regular
+expression denial of service attack via a very large number of domain name
+labels of emails and URLs.

docs/releases/4.1.10.txt

@@ -6,4 +6,9 @@ Django 4.1.10 release notes
 
 Django 4.1.10 fixes a security issue with severity "moderate" in 4.1.9.
 
-...
+CVE-2023-36053: Potential regular expression denial of service vulnerability in ``EmailValidator``/``URLValidator``
+===================================================================================================================
+
+``EmailValidator`` and ``URLValidator`` were subject to potential regular
+expression denial of service attack via a very large number of domain name
+labels of emails and URLs.

docs/releases/4.2.3.txt

@@ -7,6 +7,13 @@ Django 4.2.3 release notes
 Django 4.2.3 fixes a security issue with severity "moderate" and several bugs
 in 4.2.2.
 
+CVE-2023-36053: Potential regular expression denial of service vulnerability in ``EmailValidator``/``URLValidator``
+===================================================================================================================
+
+``EmailValidator`` and ``URLValidator`` were subject to potential regular
+expression denial of service attack via a very large number of domain name
+labels of emails and URLs.
+
 Bugfixes
 ========
 

tests/forms_tests/field_tests/test_emailfield.py

@@ -8,8 +8,9 @@ from . import FormFieldAssertionsMixin
 class EmailFieldTest(FormFieldAssertionsMixin, SimpleTestCase):
     def test_emailfield_1(self):
         f = EmailField()
+        self.assertEqual(f.max_length, 320)
         self.assertWidgetRendersTo(
-            f, '<input type="email" name="f" id="id_f" required>'
+            f, '<input type="email" name="f" id="id_f" maxlength="320" required>'
         )
         with self.assertRaisesMessage(ValidationError, "'This field is required.'"):
             f.clean("")

tests/forms_tests/tests/test_forms.py

@@ -546,7 +546,8 @@ class FormsTestCase(SimpleTestCase):
 
         f = SignupForm(auto_id=False)
         self.assertHTMLEqual(
-            str(f["email"]), '<input type="email" name="email" required>'
+            str(f["email"]),
+            '<input type="email" name="email" maxlength="320" required>',
         )
         self.assertHTMLEqual(
             str(f["get_spam"]), '<input type="checkbox" name="get_spam" required>'
@@ -555,7 +556,8 @@ class FormsTestCase(SimpleTestCase):
         f = SignupForm({"email": "test@example.com", "get_spam": True}, auto_id=False)
         self.assertHTMLEqual(
             str(f["email"]),
-            '<input type="email" name="email" value="test@example.com" required>',
+            '<input type="email" name="email" maxlength="320" value="test@example.com" '
+            "required>",
         )
         self.assertHTMLEqual(
             str(f["get_spam"]),
@@ -3521,7 +3523,7 @@ Options: <select multiple name="options" required>
             <option value="false">No</option>
             </select></li>
             <li><label for="id_email">Email:</label>
-            <input type="email" name="email" id="id_email"></li>
+            <input type="email" name="email" id="id_email" maxlength="320"></li>
             <li class="required error"><ul class="errorlist">
             <li>This field is required.</li></ul>
             <label class="required" for="id_age">Age:</label>
@@ -3543,7 +3545,7 @@ Options: <select multiple name="options" required>
             <option value="false">No</option>
             </select></p>
             <p><label for="id_email">Email:</label>
-            <input type="email" name="email" id="id_email"></p>
+            <input type="email" name="email" id="id_email" maxlength="320"></p>
             <ul class="errorlist"><li>This field is required.</li></ul>
             <p class="required error"><label class="required" for="id_age">Age:</label>
             <input type="number" name="age" id="id_age" required></p>
@@ -3563,7 +3565,7 @@ Options: <select multiple name="options" required>
 <option value="false">No</option>
 </select></td></tr>
 <tr><th><label for="id_email">Email:</label></th><td>
-<input type="email" name="email" id="id_email"></td></tr>
+<input type="email" name="email" id="id_email" maxlength="320"></td></tr>
 <tr class="required error"><th><label class="required" for="id_age">Age:</label></th>
 <td><ul class="errorlist"><li>This field is required.</li></ul>
 <input type="number" name="age" id="id_age" required></td></tr>""",
@@ -3578,7 +3580,7 @@ Options: <select multiple name="options" required>
             '<option value="unknown" selected>Unknown</option>'
             '<option value="true">Yes</option><option value="false">No</option>'
             '</select></div><div><label for="id_email">Email:</label>'
-            '<input type="email" name="email" id="id_email" /></div>'
+            '<input type="email" name="email" id="id_email" maxlength="320"/></div>'
             '<div class="required error"><label for="id_age" class="required">Age:'
             '</label><ul class="errorlist"><li>This field is required.</li></ul>'
             '<input type="number" name="age" required id="id_age" /></div>',
@@ -5094,8 +5096,9 @@ class OverrideTests(SimpleTestCase):
             '<p>Name: <input type="text" name="name" maxlength="50"></p>'
             '<div class="errorlist">'
             '<div class="error">Enter a valid email address.</div></div>'
-            '<p>Email: <input type="email" name="email" value="invalid" required></p>'
-            '<div class="errorlist">'
+            "<p>Email: "
+            '<input type="email" name="email" value="invalid" maxlength="320" required>'
+            '</p><div class="errorlist">'
             '<div class="error">This field is required.</div></div>'
             '<p>Comment: <input type="text" name="comment" required></p>',
         )

tests/validators/tests.py

@@ -106,6 +106,7 @@ VALID_URLS = [
     "ddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd"
     "ddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd"
     "ddddddddddddddddd:password@example.com:8080",
+    "http://userid:password" + "d" * 2000 + "@example.aaaaaaaaaaaaa.com",
     "http://142.42.1.1/",
     "http://142.42.1.1:8080/",
     "http://➡.ws/䨹",
@@ -236,6 +237,7 @@ INVALID_URLS = [
     "aaaaaa.com",
     "http://example.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
     "aaaaaa",
+    "http://example." + ("a" * 63 + ".") * 1000 + "com",
     "http://aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaaaaaaaaaaaaaaaa."
     "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaa"
     "aaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaa"
@@ -291,6 +293,7 @@ TEST_DATA = [
     (validate_email, "example@%s.%s.atm" % ("a" * 63, "b" * 10), None),
     (validate_email, "example@atm.%s" % ("a" * 64), ValidationError),
     (validate_email, "example@%s.atm.%s" % ("b" * 64, "a" * 63), ValidationError),
+    (validate_email, "example@%scom" % (("a" * 63 + ".") * 100), ValidationError),
     (validate_email, None, ValidationError),
     (validate_email, "", ValidationError),
     (validate_email, "abc", ValidationError),