diff --git a/keystone/auth/core.py b/keystone/auth/core.py
index 25c9c2f2fb..a6f233bc68 100644
--- a/keystone/auth/core.py
+++ b/keystone/auth/core.py
@@ -484,14 +484,20 @@ class UserMFARulesValidator(provider_api.ProviderAPIMixin):
             )
             return True
 
+        has_valid_auth_methods: bool = False
+
         for r in rules:
             # NOTE(notmorgan): We only check against the actually loaded
             # auth methods meaning that the keystone administrator may
             # disable an auth method, and a rule will still pass making it
             # impossible to accidently lock-out a subset of users with a
             # bad keystone.conf
+            # NOTE(gtema): https://bugs.launchpad.net/keystone/+bug/2102096
+            # requires that the rule containing only wrong methods is ignored
             r_set = set(r).intersection(cls._auth_methods())
-            if set(auth_methods).issuperset(r_set):
+            if r_set:
+                has_valid_auth_methods = True
+            if r_set and set(auth_methods).issuperset(r_set):
                 # Rule Matches no need to continue, return here.
                 LOG.debug(
                     'Auth methods for user `%(user_id)s`, `%(methods)s` '
@@ -506,12 +512,21 @@ class UserMFARulesValidator(provider_api.ProviderAPIMixin):
                 )
                 return True
 
-        LOG.debug(
-            'Auth methods for user `%(user_id)s`, `%(methods)s` did not '
-            'match a MFA rule in `%(rules)s`.',
-            {'user_id': user_id, 'methods': auth_methods, 'rules': rules},
-        )
-        return False
+        if has_valid_auth_methods:
+            LOG.debug(
+                'Auth methods for user `%(user_id)s`, `%(methods)s` did not '
+                'match a MFA rule in `%(rules)s`.',
+                {'user_id': user_id, 'methods': auth_methods, 'rules': rules},
+            )
+            return False
+        else:
+            LOG.debug(
+                'Auth methods for user `%(user_id)s`, `%(methods)s` did not '
+                'match a MFA rule in `%(rules)s`. Since all methods are invalid '
+                'allowing user to login to prevent lockout.',
+                {'user_id': user_id, 'methods': auth_methods, 'rules': rules},
+            )
+            return True
 
     @staticmethod
     def _parse_rule_structure(rules, user_id):
diff --git a/keystone/tests/unit/test_auth_plugin.py b/keystone/tests/unit/test_auth_plugin.py
index 917127ead8..11c9b563d7 100644
--- a/keystone/tests/unit/test_auth_plugin.py
+++ b/keystone/tests/unit/test_auth_plugin.py
@@ -21,7 +21,9 @@ from keystone.api._shared import authentication
 from keystone import auth
 from keystone.auth.plugins import base
 from keystone.auth.plugins import mapped
+from keystone.common import provider_api
 from keystone import exception
+from keystone.identity.backends import resource_options as ro
 from keystone.tests import unit
 from keystone.tests.unit.ksfixtures import auth_plugins
 
@@ -29,6 +31,7 @@ from keystone.tests.unit.ksfixtures import auth_plugins
 METHOD_NAME = 'simple_challenge_response'
 EXPECTED_RESPONSE = uuid.uuid4().hex
 DEMO_USER_ID = uuid.uuid4().hex
+PROVIDERS = provider_api.ProviderAPIs
 
 
 class SimpleChallengeResponse(base.AuthMethodHandler):
@@ -145,6 +148,98 @@ class TestAuthPluginDynamicOptions(TestAuthPlugin):
         return config_files
 
 
+class TestAuthMFA(unit.TestCase):
+    def setUp(self):
+        super().setUp()
+
+    def test_check_auth_methods_against_rules(self):
+        auth_names = ["password", "application_credential", "totp"]
+        self.useFixture(
+            auth_plugins.ConfigAuthPlugins(
+                self.config_fixture, methods=auth_names
+            )
+        )
+        self.useFixture(auth_plugins.LoadAuthPlugins(*auth_names))
+        sot = auth.core.UserMFARulesValidator
+        user_id = uuid.uuid4().hex
+        user = {
+            "id": user_id,
+            "name": uuid.uuid4().hex,
+            "enabled": True,
+            "options": {
+                ro.MFA_ENABLED_OPT.option_name: True,
+                ro.MFA_RULES_OPT.option_name: [["password", "totp"]],
+            },
+        }
+
+        identity_mock = mock.MagicMock()
+        PROVIDERS._register_provider_api("identity_api", identity_mock)
+
+        identity_mock.get_user.return_value = user
+        self.assertTrue(
+            sot.check_auth_methods_against_rules(user_id, ["password", "totp"])
+        )
+        self.assertFalse(
+            sot.check_auth_methods_against_rules(user_id, ["totp"])
+        )
+        self.assertFalse(
+            sot.check_auth_methods_against_rules(user_id, ["password"])
+        )
+
+        # Test that a rule containing invalid auth method does not lock the user out
+        identity_mock.get_user.return_value.update(
+            {
+                "options": {
+                    ro.MFA_ENABLED_OPT.option_name: True,
+                    ro.MFA_RULES_OPT.option_name: [
+                        ["password", "totp"],
+                        ["password", "fake"],
+                    ],
+                }
+            }
+        )
+        self.assertFalse(
+            sot.check_auth_methods_against_rules(user_id, ["totp"])
+        )
+        self.assertTrue(
+            sot.check_auth_methods_against_rules(user_id, ["password"])
+        )
+
+        # Test that a rule containing only invalid auth method is ignored
+        # (https://bugs.launchpad.net/keystone/+bug/2102096)
+        identity_mock.get_user.return_value.update(
+            {
+                "options": {
+                    ro.MFA_ENABLED_OPT.option_name: True,
+                    ro.MFA_RULES_OPT.option_name: [
+                        ["password", "totp"],
+                        ["fake"],
+                    ],
+                }
+            }
+        )
+        self.assertFalse(
+            sot.check_auth_methods_against_rules(user_id, ["totp"])
+        )
+        self.assertFalse(
+            sot.check_auth_methods_against_rules(user_id, ["password"])
+        )
+
+        # Test that a only rule containing only invalid auth method is not
+        # locking user out
+        identity_mock.get_user.return_value.update(
+            {
+                "options": {
+                    ro.MFA_ENABLED_OPT.option_name: True,
+                    ro.MFA_RULES_OPT.option_name: [["fake", "fake2"]],
+                }
+            }
+        )
+        self.assertTrue(
+            sot.check_auth_methods_against_rules(user_id, ["password"])
+        )
+
+
 class TestMapped(unit.TestCase):
     def config_files(self):
         config_files = super().config_files()