CVE-2026-40242: Arcane has Unauthenticated SSRF with Conditional Response Reflection in Template Fetch Endpoint

The /api/templates/fetch endpoint accepts a caller-supplied url parameter and performs a server-side HTTP GET request to that URL without authentication and without URL scheme or host validation. The server’s response is returned directly to the caller. type. This constitutes an unauthenticated SSRF vulnerability affecting any publicly reachable Arcane instance.