HomeBox is a home inventory and organization system. Prior to version 0.27.0, Homebox validates generic notifier URLs with ValidateNotifierURL before creation, update, testing, and scheduled delivery, but shoutrrr sends the request through http.DefaultClient.Do without a CheckRedirect policy that revalidates each Location target. An authenticated collection member can configure a permitted notifier host that redirects to loopback, link-local, cloud metadata, or another blocked destination, causing the follow-up request to bypass the product's SSRF policy. The flaw is reachable through POST /api/v1/notifiers/test for immediate requests and through stored notifiers during scheduled maintenance delivery. This issue is fixed in version 0.27.0.