🛡️ CVE-2026-48736 — symfony

🟠 CVSS 8.6 — High ✅ No Known Exploit CWE-184 NVD
8.6
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

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

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](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).

Credits

Symfony would like to thank tonghuaroot for reporting the issue and Nicolas Grekas for providing the fix.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. The scope is changed, meaning a successful attack can affect components beyond the vulnerable one. Rated impact: confidentiality high, integrity none, availability none.

Affected software

CVE-2026-48736 is recorded against 4 packages.

  • symfony (from 8.0.0 up to 8.0.13)
  • symfony/http-client (from 5.4.0 up to 5.4.53)
  • symfony/http-foundation (from 8.0.0 up to 8.0.13)
  • symfony/symfony (from 8.0.0 up to 8.0.13)

Timeline and source

Published on 14 July 2026 and last revised on 16 July 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from NVD.

References

github.com
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CVE-2026-48736 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity HIGH
CVSS Score 8.6
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N
CWE CWE-184
Public Exploit ✅ No
Source NVD
Published 2026-07-14
Updated 2026-08-12
Modified 2026-07-16

Affected Packages

Software From version Fixed in
symfony 8.0.0 8.0.13
symfony/http-client 5.4.0 5.4.53
symfony/http-foundation 8.0.0 8.0.13
symfony/symfony 8.0.0 8.0.13

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