[3.13] gh-130637: Add validation for numeric response data in stat() method (GH-130646) (#130763)

gh-130637: Add validation for numeric response data in `stat()` method (GH-130646)
(cherry picked from commit a42168d316)

Co-authored-by: Kanishk Pachauri <itskanishkp.py@gmail.com>
Co-authored-by: Eric V. Smith <ericvsmith@users.noreply.github.com>

Lib/test/test_poplib.py

@@ -289,6 +289,37 @@ class TestPOP3Class(TestCase):
     def test_stat(self):
         self.assertEqual(self.client.stat(), (10, 100))
 
+        original_shortcmd = self.client._shortcmd
+        def mock_shortcmd_invalid_format(cmd):
+            if cmd == 'STAT':
+                return b'+OK'
+            return original_shortcmd(cmd)
+
+        self.client._shortcmd = mock_shortcmd_invalid_format
+        with self.assertRaises(poplib.error_proto):
+            self.client.stat()
+
+        def mock_shortcmd_invalid_data(cmd):
+            if cmd == 'STAT':
+                return b'+OK abc def'
+            return original_shortcmd(cmd)
+
+        self.client._shortcmd = mock_shortcmd_invalid_data
+        with self.assertRaises(poplib.error_proto):
+            self.client.stat()
+
+        def mock_shortcmd_extra_fields(cmd):
+            if cmd == 'STAT':
+                return b'+OK 1 2 3 4 5'
+            return original_shortcmd(cmd)
+
+        self.client._shortcmd = mock_shortcmd_extra_fields
+
+        result = self.client.stat()
+        self.assertEqual(result, (1, 2))
+
+        self.client._shortcmd = original_shortcmd
+
     def test_list(self):
         self.assertEqual(self.client.list()[1:],
                          ([b'1 1', b'2 2', b'3 3', b'4 4', b'5 5'],