Guzzle: Host-Only Cookies Are Sent to Subdomains

Published as "Guzzle: Host-only cookie scope is not preserved"

medium Guzzle · Last reviewed Nov 2, 2026

CVE: CVE-2026-67355
GHSA: GHSA-wm3w-8rrp-j577
Packagist: PKSA-qxvb-2bpp-dnk6
Reported: Jul 20, 2026

Can send a parent host's session cookies to its subdomains in apps that reuse one Guzzle cookie jar across hosts.

Affected and fixed versions

In guzzlehttp/guzzle. Find the row for the version you run, and update to the release next to it.

If you run	Update to	Support
Up to 7.15.0	7.15.1	Supported

Upgrade

Run the line for the branch you are on.

composer require guzzlehttp/guzzle:^7.15.1

What this means

A cookie that a server meant only for its own host can be sent by Guzzle to that host's subdomains. If an attacker controls or can watch a subdomain, they can receive cookies such as session ids or access tokens that were meant for the parent host.

Cookies set without a Domain attribute, or with an empty one, should only go back to the exact host that set them. Guzzle stored them as if they covered the whole domain.

Who is affected

Apps on guzzlehttp/guzzle before 7.15.1 that use Guzzle's cookie support and reuse one cookie jar for a parent host and a less trusted subdomain. The Guzzle advisory points to new Client(['cookies' => true]) as a common way to share one jar. The cookie's path, Secure flag and expiry still apply. Apps that don't use Guzzle's cookies, or use a separate jar per host, aren't affected.

What to do

Update to 7.15.1 or later. The fix records host-only cookies and only sends them to the exact host.

After updating, FileCookieJar and SessionCookieJar data saved by older versions is rejected with an error. Delete or regenerate that data. Until you can update, use a separate cookie jar for each host or trust boundary.

Reported by GrahamCampbell.

Check your app with an agent

Paste this into a coding agent that can read your project, such as Claude Code, Codex or Amp. It checks your composer.lock against the versions above and tells you what to update, without changing anything.

Check whether the PHP project you have access to is affected by this security advisory, and tell me what to update. Do a read-only check: don't edit files, don't run composer update or composer require, and don't try to reproduce the flaw.

Advisory: Guzzle: Host-Only Cookies Are Sent to Subdomains (CVE-2026-67355, GHSA-wm3w-8rrp-j577)
Details: https://phpnews.net/security/guzzle/ghsa-wm3w-8rrp-j577

Affected versions, as Composer constraints:
- guzzlehttp/guzzle: <7.15.1

Fixed releases on branches that still get security fixes:
- Up to 7.15.0: update to 7.15.1

1. Find every composer.lock in the project outside vendor/ (a monorepo can have one per app) and read the installed version of each package above. Packages installed as dependencies of other packages count too.
2. Compare each installed version with its constraint: "|" separates alternative ranges, and "," means both bounds apply.
3. For each affected install, read "What this means" at https://phpnews.net/security/guzzle/ghsa-wm3w-8rrp-j577 and check whether the project meets the conditions it describes (a feature in use, a config value, a driver). Say which conditions you could check and which you couldn't.
4. Report a table: lock file | package | installed version | affected (yes, no or unknown) | conditions met (yes, no or unknown) | update to | evidence. For each affected package, give the command that would fix it, without running it: composer update <package> --with-dependencies when it is only installed as a dependency of another package, or composer require with the fixed version when composer.json requires it directly. If the installed version is on a branch with no fixed release listed, say it needs a move to a newer branch.

Sources

← All Guzzle advisories