Penpot is an open-source design and prototyping platform. Prior to 2.18.0, app.util.ssrf/blocked-address? relies on Java InetAddress predicates that do not classify NAT64, 6to4, or Teredo addresses and applies additional CIDR checks only to IPv4 values. Exploitation requires routing through a NAT64 gateway or an attacker-controlled DNS AAAA record; cloud environments with NAT64 gateways are directly exploitable. A user controlling a media import URL, or an administrator controlling a webhook URL, can then supply an IPv6 transition address that embeds a cloud-metadata, loopback, link-local, or private IPv4 target and bypasses the intended SSRF restrictions. Media import can disclose response bodies, while webhook delivery can expose response status as a network-probing side channel. This issue is fixed in version 2.18.0.