CVE-2026-42596: Gotenberg vulnerable to unauthenticated SSRF via default deny-list bypass in downloadFrom and webhook

The default deny-lists used by Gotenberg’s downloadFrom feature and webhook feature are bypassable. Because the filter is regex-based and case-sensitive, an unauthenticated attacker can supply URLs such as http://[::ffff:127.0.0.1]:... and reach loopback or private HTTP services that the default deny-list is intended to block. This crosses a real security boundary because an external caller can force the server to make outbound requests to internal-only targets.