GHSA-rjg7-r26h-cfp2: Koel: Full-read SSRF via podcast enclosure URL: isPublicHost() filter_var guard does not reject NAT64 (64:ff9b::/96) or 6to4 (2002::/16) IPv6-transition wrappers of internal IPv4

Summary Koel's outbound-URL guard App\Helpers\Network::isPublicHost() classifies an IP as "public" using PHP's filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE). That flag set does not recognise IPv6 transition-address forms that embed a private/loopback/link-local IPv4: NAT64 well-known prefix 64:ff9b::/96 (RFC 6052) and 6to4 2002::/16 (RFC 3056). An address such as 64:ff9b::7f00:1 (= 127.0.0.1), 64:ff9b::a9fe:a9fe (= 169.254.169.254, the cloud metadata endpoint), or 2002:a00:1:: (= 10.0.0.1) is reported as a public address, so the guard returns true and Koel proceeds to fetch the URL. The guard is the only SSRF defense in front of App\Values\Podcast\EpisodePlayable::createForEpisode(), which downloads a podcast episode with Http::sink($file)->get($url) and streams the response body back to the requesting user. Because an attacker fully controls the <enclosure url> of any RSS feed they host (and any authenticated user can subscribe to a feed), they can publish an enclosure whose hostname has an AAAA record that is a NAT64/6to4 wrapper of an internal IP. On hosts with NAT64 or 6to4/dual-stack routing (the standard configuration on IPv6-only AWS/GCP subnets and 6to4-relayed networks), the kernel routes the wrapper to the embedded IPv4, and Koel performs a full-read SSRF against the internal endpoint — returning the response body to the attacker. This is a server-side request forgery with full response disclosure (CWE-918) against internal services and cloud instance metadata. Vulnerable code app/Helpers/Network.php — isPublicHost() (the literal-IP branch and the per-resolved-record branch use the identical predicate): public function isPublicHost(string $host): bool { if (filter_var($host, FILTER_VALIDATE_IP)) { return ( filter_var($host, FILTER_VALIDATE_IP, FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE) !== false ); } try { $records = array_merge(dns_get_record($host, DNS_A) ?: [], dns_get_record($host, DNS_AAAA)