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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

6.3 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N · score source

EPSS

• CVE-2026-48736: 0.57% estimated exploitation activity in the next 30 days; percentile 47.26 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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::PRIVATESUBNETS 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…

Published by the source

15 Jun 2026, 17:31 UTC

Last modified by the source

15 Jun 2026, 17:31 UTC

Source last checked

26 Oct 2026, 14:49 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-38cx-cq6f-5755

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# Patch Next advisory brief: CVE-2026-48736

Advisory: Symfony: IpUtils::PRIVATE_SUBNETS Omits IPv6 Transition Forms (6to4, NAT64, Teredo, IPv4-compatible): SSRF Bypass in NoPrivateNetworkHttpClient
IDs: CVE-2026-48736, GHSA-38cx-cq6f-5755
Record: https://patchnext.com/advisories/cve-2026-48736 (revision 1, source checked 26 Oct 2026, 14:49 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: symfony/symfony 8.0.13, 7.4.13, 6.4.41, 5.4.53; symfony/http-client 5.4.53; symfony/http-foundation 8.0.13, 7.4.13, 6.4.41. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist symfony/symfony: affected >= 5.4.0, < 5.4.53; >= 6.4.0, < 6.4.41; >= 7.0.0, < 7.4.13; >= 8.0.0, < 8.0.13; fixed in 6.4.41, 8.0.13, 7.4.13, 5.4.53
- Packagist symfony/http-client: affected >= 5.4.0, < 5.4.53; fixed in 5.4.53
- Packagist symfony/http-foundation: affected >= 6.4.0, < 6.4.41; >= 7.0.0, < 7.4.13; >= 8.0.0, < 8.0.13; fixed in 6.4.41, 8.0.13, 7.4.13

## Suggested inspection (read-only)
- Packagist symfony/symfony: check the installed version with your package manager.
- Packagist symfony/http-client: check the installed version with your package manager.
- Packagist symfony/http-foundation: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on symfony/symfony, symfony/http-client, symfony/http-foundation.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-38cx-cq6f-5755 (GitHub-reviewed advisory GHSA-38cx-cq6f-5755 lists affected ranges: Packagist symfony/http-client >=5.4.0 =6.4.0 =7.0.0 =8.0.0 =5.4.0 =6.4.0 =7.0.0 =8.0.0 <8.0.13)

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