diff --git a/docs/requirements.txt b/docs/requirements.txt
index 461333f4..c98ca95e 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -2,3 +2,4 @@ mistune<2.0.0
 m2r==0.3.1
 sphinx_rtd_theme
 pan-python==0.17.0
+defusedxml==0.7.1
diff --git a/panos/userid.py b/panos/userid.py
index 675b269e..deffea53 100644
--- a/panos/userid.py
+++ b/panos/userid.py
@@ -21,6 +21,7 @@
 from copy import deepcopy
 from xml.sax.saxutils import escape, quoteattr
 
+import defusedxml.ElementTree as defused_ET
 from pan.xapi import PanXapiError
 
 import panos.errors as err
@@ -62,7 +63,7 @@ def __init__(self, device, prefix="", ignore_dup_errors=True):
         self.ignore_dup_errors = ignore_dup_errors
 
         # Build the initial uid-message
-        self._uidmessage = ET.fromstring(
+        self._uidmessage = defused_ET.fromstring(
             "<uid-message>"
             + "<version>1.0</version>"
             + "<type>update</type>"
@@ -658,7 +659,7 @@ def get_user_tags(self, user=None, prefix=None):
             msg.append("<user>{0}</user>".format(escape(user)))
         msg.append("</registered-user></object></show>")
 
-        cmd = ET.fromstring("".join(msg))
+        cmd = defused_ET.fromstring("".join(msg))
         if user is None:
             start_elm = cmd.find("./object/registered-user/all/start-point")
 
diff --git a/pyproject.toml b/pyproject.toml
index 35481fef..1fc3e9f1 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -27,6 +27,7 @@ classifiers = [
 [tool.poetry.dependencies]
 python = "^2.7 || ^3.5"
 pan-python = "^0.17.0"
+defusedxml = "^0.7.1"
 
 [tool.poetry.group.dev.dependencies]
 pytest = {version = "^5.3.2", python = "^3.5"}
diff --git a/requirements.txt b/requirements.txt
index 89baf35c..9e192200 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,3 +1,6 @@
-pan-python==0.17.0 \
+defusedxml==0.7.1 ; python_version >= "2.7" and python_version < "3.0.dev0" or python_version >= "3.5" and python_version < "4.0" \
+    --hash=sha256:1bb3032db185915b62d7c6209c5a8792be6a32ab2fedacc84e01b52c51aa3e69 \
+    --hash=sha256:a352e7e428770286cc899e2542b6cdaedb2b4953ff269a210103ec58f6198a61
+pan-python==0.17.0 ; python_version >= "2.7" and python_version < "3.0" or python_version >= "3.5" and python_version < "4.0" \
     --hash=sha256:9c074ea2f69a63996a6fefe8935d60dca61660e14715ac19d257ea9b1c41c6e2 \
     --hash=sha256:f4674e40763c46d5933244b3059a57884e4e28205ef6d0f9ce2dc2013e3db010
diff --git a/tests/test_userid.py b/tests/test_userid.py
index c2d0bf6d..5d84890a 100644
--- a/tests/test_userid.py
+++ b/tests/test_userid.py
@@ -19,8 +19,11 @@
 import unittest
 import xml.etree.ElementTree as ET
 
+import defusedxml.common
+
 import panos.firewall
 import panos.panorama
+import panos.userid
 
 
 class TestUserId(unittest.TestCase):
@@ -157,6 +160,17 @@ def test_get_group_members_escapes_group(self):
         self.assertEqual(names[0].text, evil)
         self.assertIsNone(parsed.find(".//evil"))
 
+    def test_userid_uses_defused_xml_parser(self):
+        # panos.userid must parse XML through defusedxml, not the
+        # unprotected stdlib parser, to avoid XXE/billion-laughs attacks.
+        xxe_payload = (
+            "<?xml version='1.0'?>"
+            "<!DOCTYPE foo [<!ENTITY xxe SYSTEM 'file:///etc/passwd'>]>"
+            "<uid-message>&xxe;</uid-message>"
+        )
+        with self.assertRaises(defusedxml.common.EntitiesForbidden):
+            panos.userid.defused_ET.fromstring(xxe_payload)
+
 
 if __name__ == "__main__":
     unittest.main()