CVE-2026-40168: Postiz has Server-Side Request Forgery via Redirect Bypass in /api/public/stream

Postiz is an AI social media scheduling tool. Prior to 2.21.5, the /api/public/stream endpoint is vulnerable to SSRF. Although the application validates the initially supplied URL and blocks direct private/internal hosts, it does not re-validate the final destination after HTTP redirects. As a result, an attacker can supply a public HTTPS URL that passes validation and then redirects the server-side request to an internal resource.