Gotenberg: SSRF deny-list bypass in IsPublicIP via IPv6 6to4 / NAT64 / site-local prefixes

Gotenberg is a Docker-powered stateless API for PDF files. In 8.32.0 and earlier, the IsPublicIP function in pkg/gotenberg/outbound.go does not reject the 2002::/16 6to4 prefix, the 64:ff9b::/96 and 64:ff9b:1::/48 NAT64 prefixes, the fec0::/10 deprecated site-local prefix, Teredo, and other transition prefixes that can embed or route to non-public IPv4 destinations. The addr.Unmap operation only handles IPv4-mapped IPv6 addresses, so a crafted DNS AAAA record can cause the outbound HTTP client to treat an address wrapping an internal destination such as 169.254.169.254 as public. An unauthenticated attacker can use a conversion route with WithDenyPrivateIPs enabled to reach cloud metadata services, and the Chromium URL conversion route can return the internal response as a PDF, potentially exposing cloud credentials. Exploitation requires a deployment whose host routes the relevant IPv6 prefix, such as a dual-stack or NAT64-enabled environment. This issue is fixed in version 8.33.0.