Guzzle: Malicious Server Can Flood the Cookie Jar

Published as "Guzzle: Unbounded response cookies risk denial of service"

medium Guzzle · Last reviewed Nov 2, 2026

CVE: CVE-2026-67353
GHSA: GHSA-f283-ghqc-fg79
Packagist: PKSA-bbs6-q5q9-f3t4
Reported: Jul 20, 2026

Lets a malicious server fill Guzzle's cookie jar with large cookies, using memory and breaking later requests that share the jar.

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 malicious or compromised server can send Guzzle a flood of large cookies. Guzzle stores them all and copies them into later requests, which uses memory and time and can make those requests fail. Because cookies can be set for a parent domain, a server on one subdomain can break requests to a different service that shares the same cookie jar.

The Guzzle advisory says the direct impact is on availability only.

Who is affected

Apps on guzzlehttp/guzzle before 7.15.1 that use Guzzle's built-in cookie jar, receive a response from a server an attacker controls, and keep using that jar. Updating libcurl doesn't help, since Guzzle manages these cookies itself. Apps that don't use cookies, use a separate jar for untrusted hosts, or use their own cookie jar with limits aren't affected.

What to do

Update to 7.15.1 or later. The fix limits how many cookies one response can set, how large each can be, and how large the Cookie header Guzzle sends can grow. It doesn't cap the total size of a jar built up over many responses. Until you can update, don't share a cookie jar with untrusted hosts, or clear it after an untrusted response.

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: Malicious Server Can Flood the Cookie Jar (CVE-2026-67353, GHSA-f283-ghqc-fg79)
Details: https://phpnews.net/security/guzzle/ghsa-f283-ghqc-fg79

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-f283-ghqc-fg79 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