symfony/http-client security advisory

CVE-2026-48736: IpUtils::PRIVATE_SUBNETS Omits IPv6 Transition Forms (6to4, NAT64, Teredo, IPv4-compatible): SSRF Bypass in NoPrivateNetworkHttpClient in symfony/http-client

CVE-2026-48736 is a medium-severity SSRF vulnerability in the PHP package symfony/http-client (CVSS 8.6), published 14 July 2026. It is fixed in 5.4.53; earlier versions are affected. It can be exploited without an account.

medium 8.6 published 2026-07-14 · updated 2026-07-16

Affected versions: >= 5.4.0, < 5.4.53
Fixed in: 5.4.53
Newest release: 8.1.10
Severity: Medium · CVSS 8.6
Type: Server-side request forgery (SSRF)
CWE-184, CWE-918
Exploited in the wild: Not on the CISA KEV list
checked 2026-11-04

Also affects

The same advisory covers other packages in our list. Fix whichever one your project installs.

symfony/http-foundation >= 6.4.0, < 6.4.41; >= 7.0.0, < 7.4.13; >= 8.0.0, < 8.0.13 fixed in 6.4.41, 7.4.13, 8.0.13
symfony/symfony >= 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 5.4.53, 6.4.41, 7.4.13, 8.0.13

Is your symfony/http-client version affected?

Run composer show symfony/http-client in your project, then enter the version. We check it against this and every other known symfony/http-client advisory.

Who can exploit CVE-2026-48736

Access: No account. Anyone who can send a request to an app that uses the affected code.

CVSS vector (scored by NVD): CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N

Your app is only exposed if it uses the affected part of symfony/http-client. The advisory below says which part that is. If you are not sure, upgrade anyway: it costs less than finding out.

How to fix CVE-2026-48736 in symfony/http-client

Find the installed version: composer show symfony/http-client. If you never required it yourself, composer why symfony/http-client shows which package pulls it in.
Update it: composer update symfony/http-client --with-all-dependencies. You need 5.4.53 or newer.
If Composer will not go that high, your composer.json constraint is holding it back. Widen it (for example "symfony/http-client": "^5.4.53" if you can take that version), or upgrade the package that requires it.
Run composer audit. It reads the same advisory data and should no longer list CVE-2026-48736.
Commit composer.lock and deploy it. On the server, run composer install --no-dev from the lock file, not composer update.

If you cannot upgrade yet

General hardening for SSRF issues while the upgrade waits. None of it replaces the fix.

Block outbound requests from the app server to private ranges and cloud metadata (169.254.169.254) at the firewall.
Do not pass user-supplied URLs to the affected feature.
If your app does not use the affected feature, note that in your audit, but still plan the upgrade.

The CVE-2026-48736 advisory

Symfony is a PHP framework for web and console applications and a set of reusable PHP components. From 5.4.0 to 5.4.53, 6.4.41, 7.4.13, and 8.0.13, NoPrivateNetworkHttpClient and IpUtils::PRIVATE_SUBNETS omitted IPv6 transition prefixes such as 6to4, NAT64, Teredo, and IPv4-compatible IPv6, allowing attacker-supplied URLs to represent private IPv4 targets in forms that IpUtils::isPrivateIp() did not block. This issue is fixed in versions 5.4.53, 6.4.41, 7.4.13, and 8.0.13.

Description from the CVE record, published by GitHub (the CVE Numbering Authority), via the NVD entry for CVE-2026-48736. Advisory title: “CVE-2026-48736: IpUtils::PRIVATE_SUBNETS Omits IPv6 Transition Forms (6to4, NAT64, Teredo, IPv4-compatible): SSRF Bypass in NoPrivateNetworkHttpClient”.

References

GitHub security advisory GHSA-38cx-cq6f-5755 github.com
Symfony security advisory symfony.com
Fix commit 8276536 github.com
Fix commit 85b8315 github.com
Release v5.4.53 github.com
Release v6.4.41 github.com
Release v7.4.13 github.com

Other symfony/http-client advisories

low CVE-2024-50342: Internal address and port enumeration allowed by NoPrivateNetworkHttpClient 2024-11-13

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Where this data comes from

Affected and fixed versions: the Packagist security advisories API (GitHub Advisory Database and FriendsOfPHP), the same data composer audit uses. Synced 2026-11-03.
Description, score, weakness and references: NIST National Vulnerability Database (NVD), checked 2026-11-04. This product uses data from the NVD API but is not endorsed or certified by the NVD.
Exploited-in-the-wild status: the CISA Known Exploited Vulnerabilities catalog, checked 2026-11-04.
Compiled by Daniel Lasek at Laskyr from the sources above. The summary, “who can exploit it”, “how to fix it” and hardening sections are our plain-English reading of the record and are generated from it. The quoted description is the record's own text. Spot an error? Tell us.