gh-148954: Escape methodname in xmlrpc.client.dumps() to prevent XML injection (GH-148968)

Lib/test/test_xmlrpc.py

@@ -208,6 +208,17 @@ class XMLRPCTestCase(unittest.TestCase):
         self.assertEqual(xmlrpclib.loads(strg)[0][0], value)
         self.assertEqual(xmlrpclib.loads(strg)[1], methodname)
 
+    def test_dump_escape_methodname(self):
+        payload = 'foo</methodName><injected attr="evil"/><methodName>bar'
+        s = xmlrpclib.dumps((), methodname=payload)
+        self.assertIn(
+            '<methodName>foo&lt;/methodName&gt;&lt;injected attr="evil"/&gt;'
+            '&lt;methodName&gt;bar</methodName>', s
+        )
+        self.assertNotIn('<injected attr="evil"/>', s)
+        load, m = xmlrpclib.loads(s)
+        self.assertEqual(m, payload)
+
     def test_dump_bytes(self):
         sample = b"my dog has fleas"
         self.assertEqual(sample, xmlrpclib.Binary(sample))

Lib/xmlrpc/client.py

@@ -965,7 +965,7 @@ def dumps(params, methodname=None, methodresponse=None, encoding=None,
         data = (
             xmlheader,
             "<methodCall>\n"
-            "<methodName>", methodname, "</methodName>\n",
+            "<methodName>", escape(methodname), "</methodName>\n",
             data,
             "</methodCall>\n"
             )

Misc/NEWS.d/next/Library/2026-04-24-19-54-00.gh-issue-148954.v1.rst

@@ -0,0 +1 @@
+Fix XML injection vulnerability in :func:`xmlrpc.client.dumps` where the ``methodname`` was not being escaped before interpolation into the XML body.