diff --git a/server/api/login_test.go b/server/api/login_test.go
index 18fb77ed0..5474f0b9c 100644
--- a/server/api/login_test.go
+++ b/server/api/login_test.go
@@ -250,6 +250,9 @@ func TestHandleAuth(t *testing.T) {
 
 		assert.Equal(t, http.StatusSeeOther, c.Writer.Status())
 		assert.Equal(t, "/login?error=registration_closed", c.Writer.Header().Get("Location"))
+		// a rejected login must not persist any (broken) user/org row, see #6769
+		_store.AssertNotCalled(t, "CreateUser", mock.Anything)
+		_store.AssertNotCalled(t, "OrgCreate", mock.Anything)
 	})
 
 	t.Run("should deny a user with missing org access", func(t *testing.T) {
diff --git a/server/store/datastore/migration/029_fix_zero_forge_id_user_ref.go b/server/store/datastore/migration/029_fix_zero_forge_id_user_ref.go
new file mode 100644
index 000000000..f0f580566
--- /dev/null
+++ b/server/store/datastore/migration/029_fix_zero_forge_id_user_ref.go
@@ -0,0 +1,43 @@
+// Copyright 2026 Woodpecker Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package migration
+
+import (
+	"src.techknowlogick.com/xormigrate"
+	"xorm.io/xorm"
+)
+
+// Users provisioned through the admin web UI or CLI (`admin user add`) used to
+// be stored with forge_id=0 when no forge was given, leaving them unresolvable
+// for OAuth login (they never match the real forge id, so login is rejected with
+// "registration closed"). This heals those rows by clamping them to the default
+// forge, mirroring the runtime default (api.defaultForgeID) now enforced on user
+// creation and the sibling `replaceZeroForgeIDsInOrgs` migration for orgs.
+//
+// The orgs update is repeated because a broken user's personal org is created
+// with the same forge_id=0 and could have been added after that earlier orgs
+// migration already ran.
+//
+// See https://github.com/woodpecker-ci/woodpecker/issues/6769.
+var replaceZeroForgeIDsInUsers = xormigrate.Migration{
+	ID: "replace-zero-forge-ids-in-users",
+	MigrateSession: func(sess *xorm.Session) (err error) {
+		if _, err = sess.Exec("UPDATE users SET forge_id=1 WHERE forge_id=0;"); err != nil {
+			return err
+		}
+		_, err = sess.Exec("UPDATE orgs SET forge_id=1 WHERE forge_id=0;")
+		return err
+	},
+}
diff --git a/server/store/datastore/migration/029_fix_zero_forge_id_user_ref_test.go b/server/store/datastore/migration/029_fix_zero_forge_id_user_ref_test.go
new file mode 100644
index 000000000..8f6fcea8c
--- /dev/null
+++ b/server/store/datastore/migration/029_fix_zero_forge_id_user_ref_test.go
@@ -0,0 +1,89 @@
+// Copyright 2026 Woodpecker Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package migration
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+type userV029 struct {
+	ID      int64  `xorm:"pk autoincr 'id'"`
+	ForgeID int64  `xorm:"forge_id"`
+	Login   string `xorm:"'login'"`
+	Hash    string `xorm:"'hash'"`
+}
+
+func (userV029) TableName() string { return "users" }
+
+type orgV029 struct {
+	ID      int64  `xorm:"pk autoincr 'id'"`
+	ForgeID int64  `xorm:"forge_id"`
+	Name    string `xorm:"'name'"`
+	IsUser  bool   `xorm:"is_user"`
+}
+
+func (orgV029) TableName() string { return "orgs" }
+
+func TestReplaceZeroForgeIDsInUsers(t *testing.T) {
+	engine, closeDB := testDB(t, true)
+	defer closeDB()
+
+	require.NoError(t, engine.Sync(new(userV029), new(orgV029)))
+
+	// user + personal org left with forge_id=0 by legacy CLI/web-ui provisioning
+	_, err := engine.Insert(&userV029{ForgeID: 0, Login: "broken", Hash: "h1"})
+	require.NoError(t, err)
+	_, err = engine.Insert(&orgV029{ForgeID: 0, Name: "broken", IsUser: true})
+	require.NoError(t, err)
+	// a healthy user/org already on the real forge must stay untouched
+	_, err = engine.Insert(&userV029{ForgeID: 1, Login: "healthy", Hash: "h2"})
+	require.NoError(t, err)
+	_, err = engine.Insert(&orgV029{ForgeID: 2, Name: "other-forge", IsUser: false})
+	require.NoError(t, err)
+
+	sess := engine.NewSession()
+	defer sess.Close()
+	require.NoError(t, replaceZeroForgeIDsInUsers.MigrateSession(sess))
+	require.NoError(t, sess.Commit())
+
+	zeroUsers, err := engine.Where("forge_id = 0").Count(new(userV029))
+	require.NoError(t, err)
+	assert.EqualValues(t, 0, zeroUsers, "no user should be left on forge_id=0")
+
+	zeroOrgs, err := engine.Where("forge_id = 0").Count(new(orgV029))
+	require.NoError(t, err)
+	assert.EqualValues(t, 0, zeroOrgs, "no org should be left on forge_id=0")
+
+	// the healed user is now resolvable on the default forge
+	healed := new(userV029)
+	found, err := engine.Where("login = ?", "broken").Get(healed)
+	require.NoError(t, err)
+	require.True(t, found)
+	assert.EqualValues(t, 1, healed.ForgeID)
+
+	// unrelated forge ids are untouched
+	healthy := new(userV029)
+	_, err = engine.Where("login = ?", "healthy").Get(healthy)
+	require.NoError(t, err)
+	assert.EqualValues(t, 1, healthy.ForgeID)
+
+	otherOrg := new(orgV029)
+	_, err = engine.Where("name = ?", "other-forge").Get(otherOrg)
+	require.NoError(t, err)
+	assert.EqualValues(t, 2, otherOrg.ForgeID)
+}
diff --git a/server/store/datastore/migration/migration.go b/server/store/datastore/migration/migration.go
index c34055489..0037cf5f8 100644
--- a/server/store/datastore/migration/migration.go
+++ b/server/store/datastore/migration/migration.go
@@ -57,6 +57,7 @@ var migrationTasks = []*xormigrate.Migration{
 	&fixForgeColumns,
 	&addCronField,
 	&updatePipelineStructureTagsReleases,
+	&replaceZeroForgeIDsInUsers,
 }
 
 var allBeans = []any{