Chartbrew is an open-source web application that can connect directly to databases and APIs and use the data to create charts. Prior to 5.2.1, the outbound URL guard recognized ordinary IPv4, IPv6, and IPv4-mapped IPv6 destinations but did not recognize IPv4 addresses embedded in NAT64 prefixes. The vulnerable surface is aPI Data Connection outbound requests routed through server/modules/outboundTargetPolicy.js. An authenticated user with permission to create or edit an API connection supplies an attacker-controlled hostname or redirect whose DNS answer is a NAT64 address embedding a private or link-local IPv4 destination. The policy treated the NAT64 address as public; a NAT64 gateway then