[4.2.x] Fixed CVE-2024-41989 -- Prevented excessive memory consumption in floatformat.

Thanks Elias Myllymäki for the report.

Co-authored-by: Shai Berger <shai@platonix.com>

django/template/defaultfilters.py

@@ -163,6 +163,19 @@ def floatformat(text, arg=-1):
     except ValueError:
         return input_val
 
+    _, digits, exponent = d.as_tuple()
+    try:
+        number_of_digits_and_exponent_sum = len(digits) + abs(exponent)
+    except TypeError:
+        # Exponent values can be "F", "n", "N".
+        number_of_digits_and_exponent_sum = 0
+
+    # Values with more than 200 digits, or with a large exponent, are returned "as is"
+    # to avoid high memory consumption and potential denial-of-service attacks.
+    # The cut-off of 200 is consistent with django.utils.numberformat.floatformat().
+    if number_of_digits_and_exponent_sum > 200:
+        return input_val
+
     try:
         m = int(d) - d
     except (ValueError, OverflowError, InvalidOperation):

docs/releases/4.2.15.txt

@@ -7,6 +7,15 @@ Django 4.2.15 release notes
 Django 4.2.15 fixes three security issues with severity "moderate", one
 security issue with severity "high", and a regression in 4.2.14.
 
+CVE-2024-41989: Memory exhaustion in ``django.utils.numberformat.floatformat()``
+================================================================================
+
+If :tfilter:`floatformat` received a string representation of a number in
+scientific notation with a large exponent, it could lead to significant memory
+consumption.
+
+To avoid this, decimals with more than 200 digits are now returned as is.
+
 Bugfixes
 ========
 

tests/template_tests/filter_tests/test_floatformat.py

@@ -77,6 +77,7 @@ class FunctionTests(SimpleTestCase):
         self.assertEqual(floatformat(1.5e-15, 20), "0.00000000000000150000")
         self.assertEqual(floatformat(1.5e-15, -20), "0.00000000000000150000")
         self.assertEqual(floatformat(1.00000000000000015, 16), "1.0000000000000002")
+        self.assertEqual(floatformat("1e199"), "1" + "0" * 199)
 
     def test_force_grouping(self):
         with translation.override("en"):
@@ -134,6 +135,22 @@ class FunctionTests(SimpleTestCase):
         self.assertEqual(floatformat(pos_inf), "inf")
         self.assertEqual(floatformat(neg_inf), "-inf")
         self.assertEqual(floatformat(pos_inf / pos_inf), "nan")
+        self.assertEqual(floatformat("inf"), "inf")
+        self.assertEqual(floatformat("NaN"), "NaN")
+
+    def test_too_many_digits_to_render(self):
+        cases = [
+            "1e200",
+            "1E200",
+            "1E10000000000000000",
+            "-1E10000000000000000",
+            "1e10000000000000000",
+            "-1e10000000000000000",
+            "1" + "0" * 1_000_000,
+        ]
+        for value in cases:
+            with self.subTest(value=value):
+                self.assertEqual(floatformat(value), value)
 
     def test_float_dunder_method(self):
         class FloatWrapper: