Potential denial-of-service vulnerability in XML serializer text extraction

@@ -2,7 +2,8 @@
 XML serializer.
 """
 import json
-from xml.dom import pulldom
+from contextlib import contextmanager
+from xml.dom import minidom, pulldom
 from xml.sax import handler
 from xml.sax.expatreader import ExpatParser as _ExpatParser
 
@@ -14,6 +15,25 @@
 from django.utils.xmlutils import SimplerXMLGenerator, UnserializableContentError
 
 
+@contextmanager
+def fast_cache_clearing():
+    """Workaround for performance issues in minidom document checks.
+
+    Speeds up repeated DOM operations by skipping unnecessary full traversal
+    of the DOM tree.
+    """
+    module_helper_was_lambda = False
+    if original_fn := getattr(minidom, "_in_document", None):
+        module_helper_was_lambda = original_fn.__name__ == "<lambda>"
+        if not module_helper_was_lambda:
+            minidom._in_document = lambda node: bool(node.ownerDocument)
+    try:
+        yield
+    finally:
+        if original_fn and not module_helper_was_lambda:
+            minidom._in_document = original_fn
+
+
 class Serializer(base.Serializer):
     """Serialize a QuerySet to XML."""
 
@@ -208,7 +228,8 @@ def _make_parser(self):
     def __next__(self):
         for event, node in self.event_stream:
             if event == "START_ELEMENT" and node.nodeName == "object":
-                self.event_stream.expandNode(node)
+                with fast_cache_clearing():
+                    self.event_stream.expandNode(node)
                 return self._handle_object(node)
         raise StopIteration
 
@@ -392,19 +413,25 @@ def _get_model_from_node(self, node, attr):
 
 def getInnerText(node):
     """Get all the inner text of a DOM node (recursively)."""
+    inner_text_list = getInnerTextList(node)
+    return "".join(inner_text_list)
+
+
+def getInnerTextList(node):
+    """Return a list of the inner texts of a DOM node (recursively)."""
     # inspired by https://mail.python.org/pipermail/xml-sig/2005-March/011022.html
-    inner_text = []
+    result = []
     for child in node.childNodes:
         if (
             child.nodeType == child.TEXT_NODE
             or child.nodeType == child.CDATA_SECTION_NODE
         ):
-            inner_text.append(child.data)
+            result.append(child.data)
         elif child.nodeType == child.ELEMENT_NODE:
-            inner_text.extend(getInnerText(child))
+            result.extend(getInnerTextList(child))
         else:
             pass
-    return "".join(inner_text)
+    return result
 
 
 # Below code based on Christian Heimes' defusedxml

@@ -15,6 +15,16 @@ using a suitably crafted dictionary, with dictionary expansion, as the
 ``**kwargs`` passed to :meth:`.QuerySet.annotate` or :meth:`.QuerySet.alias` on
 PostgreSQL.
 
+CVE-2025-64460: Potential denial-of-service vulnerability in XML ``Deserializer``
+=================================================================================
+
+:ref:`XML Serialization <serialization-formats-xml>` was subject to a potential
+denial-of-service attack due to quadratic time complexity when deserializing
+crafted documents containing many nested invalid elements. The internal helper
+``django.core.serializers.xml_serializer.getInnerText()`` previously
+accumulated inner text inefficiently during recursion. It now collects text per
+element, avoiding excessive resource usage.
+
 Bugfixes
 ========
 

@@ -173,6 +173,8 @@ Identifier  Information
 .. _jsonl: https://jsonlines.org/
 .. _PyYAML: https://pyyaml.org/
 
+.. _serialization-formats-xml:
+
 XML
 ---
 

@@ -1,7 +1,10 @@
+import gc
+import time
 from xml.dom import minidom
 
 from django.core import serializers
-from django.core.serializers.xml_serializer import DTDForbidden
+from django.core.serializers.xml_serializer import Deserializer, DTDForbidden
+from django.db import models
 from django.test import TestCase, TransactionTestCase
 
 from .tests import SerializersTestBase, SerializersTransactionTestBase
@@ -90,6 +93,56 @@ def test_no_dtd(self):
         with self.assertRaises(DTDForbidden):
             next(serializers.deserialize("xml", xml))
 
+    def test_crafted_xml_performance(self):
+        """The time to process invalid inputs is not quadratic."""
+
+        def build_crafted_xml(depth, leaf_text_len):
+            nested_open = "<nested>" * depth
+            nested_close = "</nested>" * depth
+            leaf = "x" * leaf_text_len
+            field_content = f"{nested_open}{leaf}{nested_close}"
+            return f"""
+                <django-objects version="1.0">
+                   <object model="contenttypes.contenttype" pk="1">
+                      <field name="app_label">{field_content}</field>
+                      <field name="model">m</field>
+                   </object>
+                </django-objects>
+            """
+
+        def deserialize(crafted_xml):
+            iterator = Deserializer(crafted_xml)
+            gc.collect()
+
+            start_time = time.perf_counter()
+            result = list(iterator)
+            end_time = time.perf_counter()
+
+            self.assertEqual(len(result), 1)
+            self.assertIsInstance(result[0].object, models.Model)
+            return end_time - start_time
+
+        def assertFactor(label, params, factor=2):
+            factors = []
+            prev_time = None
+            for depth, length in params:
+                crafted_xml = build_crafted_xml(depth, length)
+                elapsed = deserialize(crafted_xml)
+                if prev_time is not None:
+                    factors.append(elapsed / prev_time)
+                prev_time = elapsed
+
+            with self.subTest(label):
+                # Assert based on the average factor to reduce test flakiness.
+                self.assertLessEqual(sum(factors) / len(factors), factor)
+
+        assertFactor(
+            "varying depth, varying length",
+            [(50, 2000), (100, 4000), (200, 8000), (400, 16000), (800, 32000)],
+            2,
+        )
+        assertFactor("constant depth, varying length", [(100, 1), (100, 1000)], 2)
+
 
 class XmlSerializerTransactionTestCase(
     SerializersTransactionTestBase, TransactionTestCase

@@ -3,7 +3,8 @@
 """
 
 import json
-from xml.dom import pulldom
+from contextlib import contextmanager
+from xml.dom import minidom, pulldom
 from xml.sax import handler
 from xml.sax.expatreader import ExpatParser as _ExpatParser
 
@@ -15,6 +16,25 @@
 from django.utils.xmlutils import SimplerXMLGenerator, UnserializableContentError
 
 
+@contextmanager
+def fast_cache_clearing():
+    """Workaround for performance issues in minidom document checks.
+
+    Speeds up repeated DOM operations by skipping unnecessary full traversal
+    of the DOM tree.
+    """
+    module_helper_was_lambda = False
+    if original_fn := getattr(minidom, "_in_document", None):
+        module_helper_was_lambda = original_fn.__name__ == "<lambda>"
+        if not module_helper_was_lambda:
+            minidom._in_document = lambda node: bool(node.ownerDocument)
+    try:
+        yield
+    finally:
+        if original_fn and not module_helper_was_lambda:
+            minidom._in_document = original_fn
+
+
 class Serializer(base.Serializer):
     """Serialize a QuerySet to XML."""
 
@@ -210,7 +230,8 @@ def _make_parser(self):
     def __next__(self):
         for event, node in self.event_stream:
             if event == "START_ELEMENT" and node.nodeName == "object":
-                self.event_stream.expandNode(node)
+                with fast_cache_clearing():
+                    self.event_stream.expandNode(node)
                 return self._handle_object(node)
         raise StopIteration
 
@@ -397,20 +418,26 @@ def _get_model_from_node(self, node, attr):
 
 def getInnerText(node):
     """Get all the inner text of a DOM node (recursively)."""
+    inner_text_list = getInnerTextList(node)
+    return "".join(inner_text_list)
+
+
+def getInnerTextList(node):
+    """Return a list of the inner texts of a DOM node (recursively)."""
     # inspired by
     # https://mail.python.org/pipermail/xml-sig/2005-March/011022.html
-    inner_text = []
+    result = []
     for child in node.childNodes:
         if (
             child.nodeType == child.TEXT_NODE
             or child.nodeType == child.CDATA_SECTION_NODE
         ):
-            inner_text.append(child.data)
+            result.append(child.data)
         elif child.nodeType == child.ELEMENT_NODE:
-            inner_text.extend(getInnerText(child))
+            result.extend(getInnerTextList(child))
         else:
             pass
-    return "".join(inner_text)
+    return result
 
 
 # Below code based on Christian Heimes' defusedxml

@@ -15,6 +15,16 @@ using a suitably crafted dictionary, with dictionary expansion, as the
 ``**kwargs`` passed to :meth:`.QuerySet.annotate` or :meth:`.QuerySet.alias` on
 PostgreSQL.
 
+CVE-2025-64460: Potential denial-of-service vulnerability in XML ``Deserializer``
+=================================================================================
+
+:ref:`XML Serialization <serialization-formats-xml>` was subject to a potential
+denial-of-service attack due to quadratic time complexity when deserializing
+crafted documents containing many nested invalid elements. The internal helper
+``django.core.serializers.xml_serializer.getInnerText()`` previously
+accumulated inner text inefficiently during recursion. It now collects text per
+element, avoiding excessive resource usage.
+
 Bugfixes
 ========
 

@@ -15,6 +15,16 @@ using a suitably crafted dictionary, with dictionary expansion, as the
 ``**kwargs`` passed to :meth:`.QuerySet.annotate` or :meth:`.QuerySet.alias` on
 PostgreSQL.
 
+CVE-2025-64460: Potential denial-of-service vulnerability in XML ``Deserializer``
+=================================================================================
+
+:ref:`XML Serialization <serialization-formats-xml>` was subject to a potential
+denial-of-service attack due to quadratic time complexity when deserializing
+crafted documents containing many nested invalid elements. The internal helper
+``django.core.serializers.xml_serializer.getInnerText()`` previously
+accumulated inner text inefficiently during recursion. It now collects text per
+element, avoiding excessive resource usage.
+
 Bugfixes
 ========
 

@@ -15,6 +15,16 @@ using a suitably crafted dictionary, with dictionary expansion, as the
 ``**kwargs`` passed to :meth:`.QuerySet.annotate` or :meth:`.QuerySet.alias` on
 PostgreSQL.
 
+CVE-2025-64460: Potential denial-of-service vulnerability in XML ``Deserializer``
+=================================================================================
+
+:ref:`XML Serialization <serialization-formats-xml>` was subject to a potential
+denial-of-service attack due to quadratic time complexity when deserializing
+crafted documents containing many nested invalid elements. The internal helper
+``django.core.serializers.xml_serializer.getInnerText()`` previously
+accumulated inner text inefficiently during recursion. It now collects text per
+element, avoiding excessive resource usage.
+
 Bugfixes
 ========
 

@@ -173,6 +173,8 @@ Identifier  Information
 .. _jsonl: https://jsonlines.org/
 .. _PyYAML: https://pyyaml.org/
 
+.. _serialization-formats-xml:
+
 XML
 ---
 

@@ -1,11 +1,15 @@
 import json
+import time
 import unittest
 
 from django.core.serializers.base import DeserializationError, DeserializedObject
 from django.core.serializers.json import Deserializer as JsonDeserializer
 from django.core.serializers.jsonl import Deserializer as JsonlDeserializer
 from django.core.serializers.python import Deserializer
+from django.core.serializers.xml_serializer import Deserializer as XMLDeserializer
+from django.db import models
 from django.test import SimpleTestCase
+from django.test.utils import garbage_collect
 
 from .models import Author
 
@@ -133,3 +137,53 @@ def test_yaml_bytes_input(self):
 
         self.assertEqual(first_item.object, self.jane)
         self.assertEqual(second_item.object, self.joe)
+
+    def test_crafted_xml_performance(self):
+        """The time to process invalid inputs is not quadratic."""
+
+        def build_crafted_xml(depth, leaf_text_len):
+            nested_open = "<nested>" * depth
+            nested_close = "</nested>" * depth
+            leaf = "x" * leaf_text_len
+            field_content = f"{nested_open}{leaf}{nested_close}"
+            return f"""
+                <django-objects version="1.0">
+                   <object model="contenttypes.contenttype" pk="1">
+                      <field name="app_label">{field_content}</field>
+                      <field name="model">m</field>
+                   </object>
+                </django-objects>
+            """
+
+        def deserialize(crafted_xml):
+            iterator = XMLDeserializer(crafted_xml)
+            garbage_collect()
+
+            start_time = time.perf_counter()
+            result = list(iterator)
+            end_time = time.perf_counter()
+
+            self.assertEqual(len(result), 1)
+            self.assertIsInstance(result[0].object, models.Model)
+            return end_time - start_time
+
+        def assertFactor(label, params, factor=2):
+            factors = []
+            prev_time = None
+            for depth, length in params:
+                crafted_xml = build_crafted_xml(depth, length)
+                elapsed = deserialize(crafted_xml)
+                if prev_time is not None:
+                    factors.append(elapsed / prev_time)
+                prev_time = elapsed
+
+            with self.subTest(label):
+                # Assert based on the average factor to reduce test flakiness.
+                self.assertLessEqual(sum(factors) / len(factors), factor)
+
+        assertFactor(
+            "varying depth, varying length",
+            [(50, 2000), (100, 4000), (200, 8000), (400, 16000), (800, 32000)],
+            2,
+        )
+        assertFactor("constant depth, varying length", [(100, 1), (100, 1000)], 2)

@@ -3,7 +3,8 @@
 """
 
 import json
-from xml.dom import pulldom
+from contextlib import contextmanager
+from xml.dom import minidom, pulldom
 from xml.sax import handler
 from xml.sax.expatreader import ExpatParser as _ExpatParser
 
@@ -15,6 +16,25 @@
 from django.utils.xmlutils import SimplerXMLGenerator, UnserializableContentError
 
 
+@contextmanager
+def fast_cache_clearing():
+    """Workaround for performance issues in minidom document checks.
+
+    Speeds up repeated DOM operations by skipping unnecessary full traversal
+    of the DOM tree.
+    """
+    module_helper_was_lambda = False
+    if original_fn := getattr(minidom, "_in_document", None):
+        module_helper_was_lambda = original_fn.__name__ == "<lambda>"
+        if not module_helper_was_lambda:
+            minidom._in_document = lambda node: bool(node.ownerDocument)
+    try:
+        yield
+    finally:
+        if original_fn and not module_helper_was_lambda:
+            minidom._in_document = original_fn
+
+
 class Serializer(base.Serializer):
     """Serialize a QuerySet to XML."""
 
@@ -210,7 +230,8 @@ def _make_parser(self):
     def __next__(self):
         for event, node in self.event_stream:
             if event == "START_ELEMENT" and node.nodeName == "object":
-                self.event_stream.expandNode(node)
+                with fast_cache_clearing():
+                    self.event_stream.expandNode(node)
                 return self._handle_object(node)
         raise StopIteration
 
@@ -394,19 +415,25 @@ def _get_model_from_node(self, node, attr):
 
 def getInnerText(node):
     """Get all the inner text of a DOM node (recursively)."""
+    inner_text_list = getInnerTextList(node)
+    return "".join(inner_text_list)
+
+
+def getInnerTextList(node):
+    """Return a list of the inner texts of a DOM node (recursively)."""
     # inspired by https://mail.python.org/pipermail/xml-sig/2005-March/011022.html
-    inner_text = []
+    result = []
     for child in node.childNodes:
         if (
             child.nodeType == child.TEXT_NODE
             or child.nodeType == child.CDATA_SECTION_NODE
         ):
-            inner_text.append(child.data)
+            result.append(child.data)
         elif child.nodeType == child.ELEMENT_NODE:
-            inner_text.extend(getInnerText(child))
+            result.extend(getInnerTextList(child))
         else:
             pass
-    return "".join(inner_text)
+    return result
 
 
 # Below code based on Christian Heimes' defusedxml

@@ -15,6 +15,16 @@ using a suitably crafted dictionary, with dictionary expansion, as the
 ``**kwargs`` passed to :meth:`.QuerySet.annotate` or :meth:`.QuerySet.alias` on
 PostgreSQL.
 
+CVE-2025-64460: Potential denial-of-service vulnerability in XML ``Deserializer``
+=================================================================================
+
+:ref:`XML Serialization <serialization-formats-xml>` was subject to a potential
+denial-of-service attack due to quadratic time complexity when deserializing
+crafted documents containing many nested invalid elements. The internal helper
+``django.core.serializers.xml_serializer.getInnerText()`` previously
+accumulated inner text inefficiently during recursion. It now collects text per
+element, avoiding excessive resource usage.
+
 Bugfixes
 ========
 

@@ -15,6 +15,16 @@ using a suitably crafted dictionary, with dictionary expansion, as the
 ``**kwargs`` passed to :meth:`.QuerySet.annotate` or :meth:`.QuerySet.alias` on
 PostgreSQL.
 
+CVE-2025-64460: Potential denial-of-service vulnerability in XML ``Deserializer``
+=================================================================================
+
+:ref:`XML Serialization <serialization-formats-xml>` was subject to a potential
+denial-of-service attack due to quadratic time complexity when deserializing
+crafted documents containing many nested invalid elements. The internal helper
+``django.core.serializers.xml_serializer.getInnerText()`` previously
+accumulated inner text inefficiently during recursion. It now collects text per
+element, avoiding excessive resource usage.
+
 Bugfixes
 ========
 

@@ -15,6 +15,16 @@ using a suitably crafted dictionary, with dictionary expansion, as the
 ``**kwargs`` passed to :meth:`.QuerySet.annotate` or :meth:`.QuerySet.alias` on
 PostgreSQL.
 
+CVE-2025-64460: Potential denial-of-service vulnerability in XML ``Deserializer``
+=================================================================================
+
+:ref:`XML Serialization <serialization-formats-xml>` was subject to a potential
+denial-of-service attack due to quadratic time complexity when deserializing
+crafted documents containing many nested invalid elements. The internal helper
+``django.core.serializers.xml_serializer.getInnerText()`` previously
+accumulated inner text inefficiently during recursion. It now collects text per
+element, avoiding excessive resource usage.
+
 Bugfixes
 ========
 

@@ -173,6 +173,8 @@ Identifier  Information
 .. _jsonl: https://jsonlines.org/
 .. _PyYAML: https://pyyaml.org/
 
+.. _serialization-formats-xml:
+
 XML
 ---
 

@@ -1,11 +1,15 @@
 import json
+import time
 import unittest
 
 from django.core.serializers.base import DeserializationError, DeserializedObject
 from django.core.serializers.json import Deserializer as JsonDeserializer
 from django.core.serializers.jsonl import Deserializer as JsonlDeserializer
 from django.core.serializers.python import Deserializer
+from django.core.serializers.xml_serializer import Deserializer as XMLDeserializer
+from django.db import models
 from django.test import SimpleTestCase
+from django.test.utils import garbage_collect
 
 from .models import Author
 
@@ -133,3 +137,53 @@ def test_yaml_bytes_input(self):
 
         self.assertEqual(first_item.object, self.jane)
         self.assertEqual(second_item.object, self.joe)
+
+    def test_crafted_xml_performance(self):
+        """The time to process invalid inputs is not quadratic."""
+
+        def build_crafted_xml(depth, leaf_text_len):
+            nested_open = "<nested>" * depth
+            nested_close = "</nested>" * depth
+            leaf = "x" * leaf_text_len
+            field_content = f"{nested_open}{leaf}{nested_close}"
+            return f"""
+                <django-objects version="1.0">
+                   <object model="contenttypes.contenttype" pk="1">
+                      <field name="app_label">{field_content}</field>
+                      <field name="model">m</field>
+                   </object>
+                </django-objects>
+            """
+
+        def deserialize(crafted_xml):
+            iterator = XMLDeserializer(crafted_xml)
+            garbage_collect()
+
+            start_time = time.perf_counter()
+            result = list(iterator)
+            end_time = time.perf_counter()
+
+            self.assertEqual(len(result), 1)
+            self.assertIsInstance(result[0].object, models.Model)
+            return end_time - start_time
+
+        def assertFactor(label, params, factor=2):
+            factors = []
+            prev_time = None
+            for depth, length in params:
+                crafted_xml = build_crafted_xml(depth, length)
+                elapsed = deserialize(crafted_xml)
+                if prev_time is not None:
+                    factors.append(elapsed / prev_time)
+                prev_time = elapsed
+
+            with self.subTest(label):
+                # Assert based on the average factor to reduce test flakiness.
+                self.assertLessEqual(sum(factors) / len(factors), factor)
+
+        assertFactor(
+            "varying depth, varying length",
+            [(50, 2000), (100, 4000), (200, 8000), (400, 16000), (800, 32000)],
+            2,
+        )
+        assertFactor("constant depth, varying length", [(100, 1), (100, 1000)], 2)

@@ -3,7 +3,8 @@
 """
 
 import json
-from xml.dom import pulldom
+from contextlib import contextmanager
+from xml.dom import minidom, pulldom
 from xml.sax import handler
 from xml.sax.expatreader import ExpatParser as _ExpatParser
 
@@ -15,6 +16,25 @@
 from django.utils.xmlutils import SimplerXMLGenerator, UnserializableContentError
 
 
+@contextmanager
+def fast_cache_clearing():
+    """Workaround for performance issues in minidom document checks.
+
+    Speeds up repeated DOM operations by skipping unnecessary full traversal
+    of the DOM tree.
+    """
+    module_helper_was_lambda = False
+    if original_fn := getattr(minidom, "_in_document", None):
+        module_helper_was_lambda = original_fn.__name__ == "<lambda>"
+        if not module_helper_was_lambda:
+            minidom._in_document = lambda node: bool(node.ownerDocument)
+    try:
+        yield
+    finally:
+        if original_fn and not module_helper_was_lambda:
+            minidom._in_document = original_fn
+
+
 class Serializer(base.Serializer):
     """Serialize a QuerySet to XML."""
 
@@ -209,7 +229,8 @@ def _make_parser(self):
     def __next__(self):
         for event, node in self.event_stream:
             if event == "START_ELEMENT" and node.nodeName == "object":
-                self.event_stream.expandNode(node)
+                with fast_cache_clearing():
+                    self.event_stream.expandNode(node)
                 return self._handle_object(node)
         raise StopIteration
 
@@ -393,19 +414,25 @@ def _get_model_from_node(self, node, attr):
 
 def getInnerText(node):
     """Get all the inner text of a DOM node (recursively)."""
+    inner_text_list = getInnerTextList(node)
+    return "".join(inner_text_list)
+
+
+def getInnerTextList(node):
+    """Return a list of the inner texts of a DOM node (recursively)."""
     # inspired by https://mail.python.org/pipermail/xml-sig/2005-March/011022.html
-    inner_text = []
+    result = []
     for child in node.childNodes:
         if (
             child.nodeType == child.TEXT_NODE
             or child.nodeType == child.CDATA_SECTION_NODE
         ):
-            inner_text.append(child.data)
+            result.append(child.data)
         elif child.nodeType == child.ELEMENT_NODE:
-            inner_text.extend(getInnerText(child))
+            result.extend(getInnerTextList(child))
         else:
             pass
-    return "".join(inner_text)
+    return result
 
 
 # Below code based on Christian Heimes' defusedxml

@@ -15,6 +15,16 @@ using a suitably crafted dictionary, with dictionary expansion, as the
 ``**kwargs`` passed to :meth:`.QuerySet.annotate` or :meth:`.QuerySet.alias` on
 PostgreSQL.
 
+CVE-2025-64460: Potential denial-of-service vulnerability in XML ``Deserializer``
+=================================================================================
+
+:ref:`XML Serialization <serialization-formats-xml>` was subject to a potential
+denial-of-service attack due to quadratic time complexity when deserializing
+crafted documents containing many nested invalid elements. The internal helper
+``django.core.serializers.xml_serializer.getInnerText()`` previously
+accumulated inner text inefficiently during recursion. It now collects text per
+element, avoiding excessive resource usage.
+
 Bugfixes
 ========
 

@@ -15,6 +15,16 @@ using a suitably crafted dictionary, with dictionary expansion, as the
 ``**kwargs`` passed to :meth:`.QuerySet.annotate` or :meth:`.QuerySet.alias` on
 PostgreSQL.
 
+CVE-2025-64460: Potential denial-of-service vulnerability in XML ``Deserializer``
+=================================================================================
+
+:ref:`XML Serialization <serialization-formats-xml>` was subject to a potential
+denial-of-service attack due to quadratic time complexity when deserializing
+crafted documents containing many nested invalid elements. The internal helper
+``django.core.serializers.xml_serializer.getInnerText()`` previously
+accumulated inner text inefficiently during recursion. It now collects text per
+element, avoiding excessive resource usage.
+
 Bugfixes
 ========
 

@@ -173,6 +173,8 @@ Identifier  Information
 .. _jsonl: https://jsonlines.org/
 .. _PyYAML: https://pyyaml.org/
 
+.. _serialization-formats-xml:
+
 XML
 ---
 

@@ -1,7 +1,10 @@
+import gc
+import time
 from xml.dom import minidom
 
 from django.core import serializers
-from django.core.serializers.xml_serializer import DTDForbidden
+from django.core.serializers.xml_serializer import Deserializer, DTDForbidden
+from django.db import models
 from django.test import TestCase, TransactionTestCase
 
 from .tests import SerializersTestBase, SerializersTransactionTestBase
@@ -90,6 +93,56 @@ def test_no_dtd(self):
         with self.assertRaises(DTDForbidden):
             next(serializers.deserialize("xml", xml))
 
+    def test_crafted_xml_performance(self):
+        """The time to process invalid inputs is not quadratic."""
+
+        def build_crafted_xml(depth, leaf_text_len):
+            nested_open = "<nested>" * depth
+            nested_close = "</nested>" * depth
+            leaf = "x" * leaf_text_len
+            field_content = f"{nested_open}{leaf}{nested_close}"
+            return f"""
+                <django-objects version="1.0">
+                   <object model="contenttypes.contenttype" pk="1">
+                      <field name="app_label">{field_content}</field>
+                      <field name="model">m</field>
+                   </object>
+                </django-objects>
+            """
+
+        def deserialize(crafted_xml):
+            iterator = Deserializer(crafted_xml)
+            gc.collect()
+
+            start_time = time.perf_counter()
+            result = list(iterator)
+            end_time = time.perf_counter()
+
+            self.assertEqual(len(result), 1)
+            self.assertIsInstance(result[0].object, models.Model)
+            return end_time - start_time
+
+        def assertFactor(label, params, factor=2):
+            factors = []
+            prev_time = None
+            for depth, length in params:
+                crafted_xml = build_crafted_xml(depth, length)
+                elapsed = deserialize(crafted_xml)
+                if prev_time is not None:
+                    factors.append(elapsed / prev_time)
+                prev_time = elapsed
+
+            with self.subTest(label):
+                # Assert based on the average factor to reduce test flakiness.
+                self.assertLessEqual(sum(factors) / len(factors), factor)
+
+        assertFactor(
+            "varying depth, varying length",
+            [(50, 2000), (100, 4000), (200, 8000), (400, 16000), (800, 32000)],
+            2,
+        )
+        assertFactor("constant depth, varying length", [(100, 1), (100, 1000)], 2)
+
 
 class XmlSerializerTransactionTestCase(
     SerializersTransactionTestBase, TransactionTestCase