GHSA-38cx-cq6f-5755 Symfony: IpUtils::PRIVATE_SUBNETS Omits IPv6 Transition Forms (6to4, NAT64, Teredo, IPv4-compatible): SSRF Bypass in NoPrivateNetworkHttpClient

• Packagist symfony/http-client: >= 5.4.0, < 5.4.53 → fixed in 5.4.53 • Packagist symfony/http-foundation: >= 6.4.0, < 6.4.41 → fixed in 6.4.41 • Packagist symfony/http-foundation: >= 7.0.0, < 7.4.13 → fixed in 7.4.13 • Packagist symfony/http-foundation: >= 8.0.0, < 8.0.13 → fixed in 8.0.13 • Packagist symfony/symfony: >= 5.4.0, < 5.4.53 → fixed in 5.4.53 • Packagist symfony/symfony: >= 6.4.0, < 6.4.41 → fixed in 6.4.41 • Packagist symfony/symfony: >= 7.0.0, < 7.4.13 → fixed in 7.4.13 • Packagist symfony/symfony: >= 8.0.0, < 8.0.13 → fixed in 8.0.13

Description `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). `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. Real-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. Resolution The 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. The patches for this issue are available here for branch 5.4 and here for branch 6.4 (and forward-ported to 7.4, 8.0 and 8.1). Credits Symfony would like to thank tonghuaroot for reporting the issue and Nicolas Grekas for providing the fix.