{"id":"CVE-2026-48736","aliases":["GHSA-38cx-cq6f-5755"],"url":"https://o3.security/vulnerability/CVE-2026-48736","summary":"Symfony: IpUtils::PRIVATE_SUBNETS Omits IPv6 Transition Forms (6to4, NAT64, Teredo, IPv4-compatible): SSRF Bypass in NoPrivateNetworkHttpClient","details":"### Description\n\n`Symfony\\Component\\HttpClient\\NoPrivateNetworkHttpClient` is documented as a decorator that blocks requests to private networks by default. The list of blocked subnets (`Symfony\\Component\\HttpFoundation\\IpUtils::PRIVATE_SUBNETS` on 6.4+, a private constant in `NoPrivateNetworkHttpClient` on 5.4) enumerates RFC1918, loopback, link-local and IPv4-mapped IPv6 (`::ffff:0:0/96`) prefixes, but omits the remaining IPv6 transition forms that can embed a private IPv4 destination: 6to4 (`2002::/16`, RFC 3056), Teredo (`2001::/32`, RFC 4380), NAT64 (`64:ff9b::/96`, RFC 6052 and `64:ff9b:1::/48`, RFC 8215) and IPv4-compatible IPv6 (`::/96`, RFC 4291 §2.5.5.1).\n\n`IpUtils::checkIp6()` is a pure bitwise CIDR comparison against the constants list and never extracts the embedded IPv4, so an attacker who can supply a URL writes the loopback / RFC1918 IPv4 target as e.g. `http://[2002:7f00:1::]/` (6to4 → 127.0.0.1), `http://[64:ff9b::7f00:1]/` (NAT64 → 127.0.0.1), `http://[::7f00:1]/` (IPv4-compatible → 127.0.0.1) or `http://[2001::1]/` (Teredo). `IpUtils::isPrivateIp()` returns `false` and `NoPrivateNetworkHttpClient` dispatches the request.\n\nReal-world reachability of the embedded IPv4 depends on the deploy's IPv6 routing (6to4 tunnel interface, upstream NAT64 gateway, kernel handling of IPv4-compatible addresses), but the security boundary the decorator promises — the dispatch decision — is crossed regardless of whether the packet ultimately lands on the embedded IPv4.\n\n### Resolution\n\nThe private-subnet list now includes `::/96`, `2002::/16`, `2001::/32`, `64:ff9b::/96` and `64:ff9b:1::/48`. Blanket blocking of these prefixes matches the policy applied by Chromium and Mozilla's Private Network Access; server-side HTTPS APIs are not legitimately published on these prefixes.\n\nThe patches for this issue are available [here](https://github.com/symfony/symfony/commit/82765368cf74177c36613575182f168a2eb765b2) for branch 5.4 and [here](https://github.com/symfony/symfony/commit/85b831555be8ea1f43bf01078afe87bc4c92f65e) for branch 6.4 (and forward-ported to 7.4, 8.0 and 8.1).\n\n### Credits\n\nSymfony would like to thank tonghuaroot for reporting the issue and Nicolas Grekas for providing the fix.","published":"2026-07-14T19:09:30.260Z","modified":"2026-08-12T03:51:22.070798902Z","cvss":null,"epss":{"score":0.0057,"percentile":0.45773,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Packagist","name":"symfony/http-client","fixedVersion":"5.4.53"},{"ecosystem":"Packagist","name":"symfony/http-foundation","fixedVersion":"6.4.41"},{"ecosystem":"Packagist","name":"symfony/http-foundation","fixedVersion":"7.4.13"},{"ecosystem":"Packagist","name":"symfony/http-foundation","fixedVersion":"8.0.13"},{"ecosystem":"Packagist","name":"symfony/symfony","fixedVersion":"5.4.53"},{"ecosystem":"Packagist","name":"symfony/symfony","fixedVersion":"6.4.41"},{"ecosystem":"Packagist","name":"symfony/symfony","fixedVersion":"7.4.13"},{"ecosystem":"Packagist","name":"symfony/symfony","fixedVersion":"8.0.13"}],"fix":{"url":"https://github.com/symfony/symfony/commit/82765368cf74177c36613575182f168a2eb765b2","label":"symfony/symfony@8276536"},"references":[{"type":"WEB","url":"https://github.com/symfony/symfony/releases/tag/v5.4.53"},{"type":"WEB","url":"https://github.com/symfony/symfony/releases/tag/v6.4.41"},{"type":"WEB","url":"https://github.com/symfony/symfony/releases/tag/v7.4.13"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/48xxx/CVE-2026-48736.json"},{"type":"ADVISORY","url":"https://github.com/symfony/symfony/security/advisories/GHSA-38cx-cq6f-5755"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-48736"},{"type":"FIX","url":"https://github.com/symfony/symfony/commit/82765368cf74177c36613575182f168a2eb765b2"},{"type":"FIX","url":"https://github.com/symfony/symfony/commit/85b831555be8ea1f43bf01078afe87bc4c92f65e"},{"type":"WEB","url":"https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/http-client/CVE-2026-48736.yaml"},{"type":"WEB","url":"https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/http-foundation/CVE-2026-48736.yaml"},{"type":"WEB","url":"https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/symfony/CVE-2026-48736.yaml"},{"type":"PACKAGE","url":"https://github.com/symfony/symfony"},{"type":"WEB","url":"https://symfony.com/cve-2026-48736"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:22.070798902Z"}}