diff --git a/ironic/api/controllers/v1/utils.py b/ironic/api/controllers/v1/utils.py
index 1156fa6061..7fe557476b 100644
--- a/ironic/api/controllers/v1/utils.py
+++ b/ironic/api/controllers/v1/utils.py
@@ -18,6 +18,7 @@ from http import client as http_client
 import inspect
 import io
 import re
+import string
 
 import jsonpatch
 import jsonschema
@@ -932,6 +933,10 @@ _CONFIG_DRIVE_SCHEMA = {
 }
 
 
+# Include newlines and spaces since they're common in base64 values.
+_B64_ALPHABET = frozenset(string.ascii_letters + string.digits + '+/=\n\r\t ')
+
+
 def check_allow_configdrive(target, configdrive=None):
     if not configdrive:
         return
@@ -969,6 +974,19 @@ def check_allow_configdrive(target, configdrive=None):
                         'opr': versions.MINOR_59_CONFIGDRIVE_VENDOR_DATA}
             raise exception.ClientSideError(
                 msg, status_code=http_client.BAD_REQUEST)
+    else:
+        # : is not a valid base64 symbol, so we can use this simple check
+        if '://' in configdrive:
+            return
+
+        # This is not 100% robust but it does solve the case of invalid
+        # JSON assumed to be a base64 string.
+        letters = set(configdrive)
+        if letters - _B64_ALPHABET:
+            msg = _('Invalid configdrive format: it is neither a JSON, nor '
+                    'a URL, nor a base64 string')
+            raise exception.ClientSideError(
+                msg, status_code=http_client.BAD_REQUEST)
 
 
 def check_allow_filter_by_fault(fault):
diff --git a/ironic/tests/unit/api/controllers/v1/test_node.py b/ironic/tests/unit/api/controllers/v1/test_node.py
index eb98732393..d3bff3f8b4 100644
--- a/ironic/tests/unit/api/controllers/v1/test_node.py
+++ b/ironic/tests/unit/api/controllers/v1/test_node.py
@@ -5007,14 +5007,44 @@ class TestPut(test_api_base.BaseApiTest):
                                               deploy_steps=None)
 
     def test_provision_with_deploy_configdrive(self):
+        FAKE_CD = """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 """
         ret = self.put_json('/nodes/%s/states/provision' % self.node.uuid,
-                            {'target': states.ACTIVE, 'configdrive': 'foo'})
+                            {'target': states.ACTIVE,
+                             'configdrive': FAKE_CD})
         self.assertEqual(http_client.ACCEPTED, ret.status_code)
         self.assertEqual(b'', ret.body)
         self.mock_dnd.assert_called_once_with(context=mock.ANY,
                                               node_id=self.node.uuid,
                                               rebuild=False,
-                                              configdrive='foo',
+                                              configdrive=FAKE_CD,
+                                              topic='test-topic',
+                                              deploy_steps=None)
+        # Check location header
+        self.assertIsNotNone(ret.location)
+        expected_location = '/v1/nodes/%s/states' % self.node.uuid
+        self.assertEqual(urlparse.urlparse(ret.location).path,
+                         expected_location)
+
+    def test_provision_with_deploy_configdrive_url(self):
+        ret = self.put_json('/nodes/%s/states/provision' % self.node.uuid,
+                            {'target': states.ACTIVE,
+                             'configdrive': 'http://example.com'})
+        self.assertEqual(http_client.ACCEPTED, ret.status_code)
+        self.assertEqual(b'', ret.body)
+        self.mock_dnd.assert_called_once_with(context=mock.ANY,
+                                              node_id=self.node.uuid,
+                                              rebuild=False,
+                                              configdrive='http://example.com',
                                               topic='test-topic',
                                               deploy_steps=None)
         # Check location header
@@ -5055,10 +5085,20 @@ class TestPut(test_api_base.BaseApiTest):
                                               topic='test-topic',
                                               deploy_steps=None)
 
-    def test_provision_with_deploy_configdrive_as_dict_unsupported(self):
+    def test_provision_with_deploy_configdrive_invalid_type(self):
         ret = self.put_json('/nodes/%s/states/provision' % self.node.uuid,
                             {'target': states.ACTIVE,
-                             'configdrive': {'user_data': 'foo'}},
+                             'configdrive': ["aabb"]},
+                            headers={api_base.Version.string: '1.60'},
+                            expect_errors=True)
+        self.assertEqual(http_client.BAD_REQUEST, ret.status_code)
+
+    def test_provision_with_deploy_configdrive_not_base64(self):
+        ret = self.put_json('/nodes/%s/states/provision' % self.node.uuid,
+                            {'target': states.ACTIVE,
+                             # Simulate invalid JSON provided to CLI
+                             'configdrive': '{"meta_data": '},
+                            headers={api_base.Version.string: '1.60'},
                             expect_errors=True)
         self.assertEqual(http_client.BAD_REQUEST, ret.status_code)
 
diff --git a/releasenotes/notes/configdrive-format-1b11f6068bd742cd.yaml b/releasenotes/notes/configdrive-format-1b11f6068bd742cd.yaml
new file mode 100644
index 0000000000..5410831d3d
--- /dev/null
+++ b/releasenotes/notes/configdrive-format-1b11f6068bd742cd.yaml
@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    Rejects ``configdrive`` that is not a JSON, a URL or a base64 string.
+    Previously invalid JSON supplied to ironicclient could end up accepted
+    as a configdrive, which would cause a failure much later.