diff --git a/pkg/services/authn/authnimpl/sync/user_sync.go b/pkg/services/authn/authnimpl/sync/user_sync.go
index 1f6362ec1a5..3d092bb968d 100644
--- a/pkg/services/authn/authnimpl/sync/user_sync.go
+++ b/pkg/services/authn/authnimpl/sync/user_sync.go
@@ -156,8 +156,8 @@ func (s *UserSync) ValidateUserProvisioningHook(ctx context.Context, id *authn.I
 
 	// Validate the provisioned user.ExternalUID with the authinfo.ExternalUID
 	if usr.IsProvisioned {
-		// The user is provisioned via SAML and the identity is empty, meaning this request is not from the SAML auth flow
-		if authInfo.AuthModule == login.SAMLAuthModule && authInfo.ExternalUID != "" && id.ExternalUID == "" {
+		// Allow non-SAML requests for SAML-provisioned users to proceed if incoming ExternalUID is empty (e.g. session access).
+		if authInfo.AuthModule == login.SAMLAuthModule && id.AuthenticatedBy != login.SAMLAuthModule && authInfo.ExternalUID != "" && id.ExternalUID == "" {
 			log.Debug("Skipping ExternalUID validation for non-SAML request to SAML-provisioned user")
 			return nil
 		}
diff --git a/pkg/services/authn/authnimpl/sync/user_sync_test.go b/pkg/services/authn/authnimpl/sync/user_sync_test.go
index 266ba3a739a..6f565a974fc 100644
--- a/pkg/services/authn/authnimpl/sync/user_sync_test.go
+++ b/pkg/services/authn/authnimpl/sync/user_sync_test.go
@@ -439,6 +439,94 @@ func TestUserSync_SyncUserHook(t *testing.T) {
 				},
 			},
 		},
+		{
+			name: "SyncUserHook: Provisioned user, Incoming ExternalUID is empty, DB ExternalUID non-empty - expect errEmptyExternalUID",
+			fields: fields{
+				userService:     &usertest.FakeUserService{ExpectedUser: &user.User{ID: 1, IsProvisioned: true}},
+				authInfoService: &authinfotest.FakeService{ExpectedUserAuth: &login.UserAuth{UserId: 1, AuthModule: login.SAMLAuthModule, ExternalUID: "db-uid"}},
+				quotaService:    &quotatest.FakeQuotaService{},
+			},
+			args: args{
+				ctx: context.Background(),
+				id: &authn.Identity{
+					AuthID:          "1",
+					AuthenticatedBy: login.SAMLAuthModule,
+					ExternalUID:     "",
+					ClientParams:    authn.ClientParams{SyncUser: true},
+				},
+			},
+			wantErr: true, // Expecting errEmptyExternalUID
+		},
+		{
+			name: "SyncUserHook: Provisioned user, Incoming ExternalUID is empty, DB ExternalUID also empty - expect errEmptyExternalUID",
+			fields: fields{
+				userService:     &usertest.FakeUserService{ExpectedUser: &user.User{ID: 1, IsProvisioned: true}},
+				authInfoService: &authinfotest.FakeService{ExpectedUserAuth: &login.UserAuth{UserId: 1, AuthModule: login.SAMLAuthModule, ExternalUID: ""}}, // DB empty
+				quotaService:    &quotatest.FakeQuotaService{},
+			},
+			args: args{
+				ctx: context.Background(),
+				id: &authn.Identity{
+					AuthID:          "1",
+					AuthenticatedBy: login.SAMLAuthModule,
+					ExternalUID:     "",
+					ClientParams:    authn.ClientParams{SyncUser: true},
+				},
+			},
+			wantErr: true, // Expecting errEmptyExternalUID
+		},
+		{
+			name: "SyncUserHook: Provisioned user, Incoming and DB ExternalUIDs non-empty and mismatch - expect errMismatchedExternalUID",
+			fields: fields{
+				userService:     &usertest.FakeUserService{ExpectedUser: &user.User{ID: 1, IsProvisioned: true}},
+				authInfoService: &authinfotest.FakeService{ExpectedUserAuth: &login.UserAuth{UserId: 1, AuthModule: login.SAMLAuthModule, ExternalUID: "db-uid"}},
+				quotaService:    &quotatest.FakeQuotaService{},
+			},
+			args: args{
+				ctx: context.Background(),
+				id: &authn.Identity{
+					AuthID:          "1",
+					AuthenticatedBy: login.SAMLAuthModule,
+					ExternalUID:     "incoming-uid",
+					ClientParams:    authn.ClientParams{SyncUser: true},
+				},
+			},
+			wantErr: true, // Expecting errMismatchedExternalUID
+		},
+		{
+			name: "SyncUserHook: Provisioned user, Incoming and DB ExternalUIDs non-empty and match - expect success",
+			fields: fields{
+				userService:     &usertest.FakeUserService{ExpectedUser: &user.User{ID: 1, Login: "user1", Email: "user1@test.com", Name: "User One", IsProvisioned: true}},
+				authInfoService: &authinfotest.FakeService{ExpectedUserAuth: &login.UserAuth{UserId: 1, AuthModule: login.SAMLAuthModule, AuthId: "1", ExternalUID: "matching-uid"}},
+				quotaService:    &quotatest.FakeQuotaService{},
+			},
+			args: args{
+				ctx: context.Background(),
+				id: &authn.Identity{
+					AuthID:          "1",
+					AuthenticatedBy: login.SAMLAuthModule,
+					Login:           "user1",
+					Email:           "user1@test.com",
+					Name:            "User One",
+					ExternalUID:     "matching-uid",
+					ClientParams:    authn.ClientParams{SyncUser: true},
+				},
+			},
+			wantErr: false,
+			wantID: &authn.Identity{
+				ID:              "1",
+				UID:             "",
+				Type:            claims.TypeUser,
+				AuthID:          "1",
+				AuthenticatedBy: login.SAMLAuthModule,
+				Login:           "user1",
+				Email:           "user1@test.com",
+				Name:            "User One",
+				ExternalUID:     "matching-uid",
+				IsGrafanaAdmin:  ptrBool(false),
+				ClientParams:    authn.ClientParams{SyncUser: true},
+			},
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -812,12 +900,118 @@ func TestUserSync_ValidateUserProvisioningHook(t *testing.T) {
 				return userSyncService
 			},
 			identity: &authn.Identity{
-				AuthenticatedBy: login.SAMLAuthModule,
+				AuthenticatedBy: login.GenericOAuthModule,
+				AuthID:          "1",
+				ExternalUID:     "",
+			},
+			expectedErr: nil,
+		},
+		{
+			desc: "ValidateProvisioning: DB ExternalUID is empty, Incoming ExternalUID is empty - expect mismatch (stricter logic)",
+			userSyncServiceSetup: func() *UserSync {
+				userSyncService := initUserSyncService()
+				userSyncService.isUserProvisioningEnabled = true
+				userSyncService.userService = &usertest.FakeUserService{ExpectedUser: &user.User{ID: 1, IsProvisioned: true}}
+				userSyncService.authInfoService = &authinfotest.FakeService{ExpectedUserAuth: &login.UserAuth{UserId: 1, AuthModule: login.SAMLAuthModule, ExternalUID: ""}}
+				return userSyncService
+			},
+			identity:    &authn.Identity{AuthenticatedBy: login.SAMLAuthModule, AuthID: "1", ExternalUID: ""},
+			expectedErr: errUserExternalUIDMismatch,
+		},
+		{
+			desc: "ValidateProvisioning: DB ExternalUID non-empty, Incoming ExternalUID is empty - expect mismatch",
+			userSyncServiceSetup: func() *UserSync {
+				userSyncService := initUserSyncService()
+				userSyncService.isUserProvisioningEnabled = true
+				userSyncService.userService = &usertest.FakeUserService{ExpectedUser: &user.User{ID: 1, IsProvisioned: true}}
+				userSyncService.authInfoService = &authinfotest.FakeService{ExpectedUserAuth: &login.UserAuth{UserId: 1, AuthModule: login.SAMLAuthModule, ExternalUID: "valid-uid"}}
+				return userSyncService
+			},
+			identity:    &authn.Identity{AuthenticatedBy: login.SAMLAuthModule, AuthID: "1", ExternalUID: ""},
+			expectedErr: errUserExternalUIDMismatch,
+		},
+		{
+			desc: "ValidateProvisioning: DB ExternalUID is empty, Incoming ExternalUID non-empty - expect mismatch (stricter logic)",
+			userSyncServiceSetup: func() *UserSync {
+				userSyncService := initUserSyncService()
+				userSyncService.isUserProvisioningEnabled = true
+				userSyncService.userService = &usertest.FakeUserService{ExpectedUser: &user.User{ID: 1, IsProvisioned: true}}
+				userSyncService.authInfoService = &authinfotest.FakeService{ExpectedUserAuth: &login.UserAuth{UserId: 1, AuthModule: login.SAMLAuthModule, ExternalUID: ""}}
+				return userSyncService
+			},
+			identity:    &authn.Identity{AuthenticatedBy: login.SAMLAuthModule, AuthID: "1", ExternalUID: "valid-uid"},
+			expectedErr: errUserExternalUIDMismatch,
+		},
+		{
+			desc: "ValidateProvisioning: DB and Incoming ExternalUIDs non-empty and mismatch - expect mismatch",
+			userSyncServiceSetup: func() *UserSync {
+				userSyncService := initUserSyncService()
+				userSyncService.isUserProvisioningEnabled = true
+				userSyncService.userService = &usertest.FakeUserService{ExpectedUser: &user.User{ID: 1, IsProvisioned: true}}
+				userSyncService.authInfoService = &authinfotest.FakeService{ExpectedUserAuth: &login.UserAuth{UserId: 1, AuthModule: login.SAMLAuthModule, ExternalUID: "db-uid"}}
+				return userSyncService
+			},
+			identity:    &authn.Identity{AuthenticatedBy: login.SAMLAuthModule, AuthID: "1", ExternalUID: "incoming-uid"},
+			expectedErr: errUserExternalUIDMismatch,
+		},
+		{
+			desc: "it should skip ExternalUID validation for a SAML-provisioned user accessed by a non-SAML method with an empty incoming ExternalUID",
+			userSyncServiceSetup: func() *UserSync {
+				userSyncService := initUserSyncService()
+				userSyncService.allowNonProvisionedUsers = false
+				userSyncService.isUserProvisioningEnabled = true
+				userSyncService.userService = &usertest.FakeUserService{
+					ExpectedUser: &user.User{
+						ID:            1,
+						IsProvisioned: true,
+					},
+				}
+				userSyncService.authInfoService = &authinfotest.FakeService{
+					ExpectedUserAuth: &login.UserAuth{
+						UserId:      1,
+						AuthModule:  login.SAMLAuthModule,
+						AuthId:      "1",
+						ExternalUID: "saml-originated-uid",
+					},
+				}
+				return userSyncService
+			},
+			identity: &authn.Identity{
+				AuthenticatedBy: login.GenericOAuthModule,
 				AuthID:          "1",
 				ExternalUID:     "",
 			},
 			expectedErr: nil,
 		},
+		{
+			desc: "it should fail validation when a provisioned user is accessed by SAML with an empty incoming ExternalUID",
+			userSyncServiceSetup: func() *UserSync {
+				userSyncService := initUserSyncService()
+				userSyncService.allowNonProvisionedUsers = false
+				userSyncService.isUserProvisioningEnabled = true
+				userSyncService.userService = &usertest.FakeUserService{
+					ExpectedUser: &user.User{
+						ID:            1,
+						IsProvisioned: true,
+					},
+				}
+				userSyncService.authInfoService = &authinfotest.FakeService{
+					ExpectedUserAuth: &login.UserAuth{
+						UserId:      1,
+						AuthModule:  login.SAMLAuthModule,
+						AuthId:      "1",
+						ExternalUID: "saml-originated-uid",
+					},
+				}
+				return userSyncService
+			},
+			identity: &authn.Identity{
+				AuthenticatedBy: login.SAMLAuthModule,
+				AuthID:          "1",
+				ExternalUID:     "",
+			},
+			expectedErr: errUserExternalUIDMismatch.Errorf("the provisioned user.ExternalUID does not match the authinfo.ExternalUID"),
+		},
 	}
 
 	for _, tt := range tests {