guzzlehttp/guzzle security advisory

CVE-2026-67353: Guzzle: Unbounded response cookies risk denial of service

CVE-2026-67353 is a medium-severity denial of service vulnerability in the PHP package guzzlehttp/guzzle (CVSS 5.3), published 1 August 2026. It is fixed in 7.15.1; earlier versions are affected. It can be exploited without an account.

medium 5.3 published 2026-08-01 · updated 2026-10-08

Affected versions: < 7.15.1
Fixed in: 7.15.1
Newest release: 8.3.1
Severity: Medium · CVSS 5.3
Type: Denial of service
CWE-770
Exploited in the wild: Not on the CISA KEV list
checked 2026-11-04

Is your guzzlehttp/guzzle version affected?

Run composer show guzzlehttp/guzzle in your project, then enter the version. We check it against this and every other known guzzlehttp/guzzle advisory.

Who can exploit CVE-2026-67353

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

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

Your app is only exposed if it uses the affected part of guzzlehttp/guzzle. 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-2026-67353 in guzzlehttp/guzzle

Find the installed version: composer show guzzlehttp/guzzle. If you never required it yourself, composer why guzzlehttp/guzzle shows which package pulls it in.
Update it: composer update guzzlehttp/guzzle --with-all-dependencies. You need 7.15.1 or newer.
If Composer will not go that high, your composer.json constraint is holding it back. Widen it (for example "guzzlehttp/guzzle": "^7.15.1" 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-2026-67353.
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 denial of service issues while the upgrade waits. None of it replaces the fix.

Rate-limit the affected endpoint and cap request body, header and upload sizes at the web server.
If your app does not use the affected feature, note that in your audit, but still plan the upgrade.

The CVE-2026-67353 advisory

guzzlehttp/guzzle versions before 7.15.1 contain a denial of service vulnerability in the CookieJar that accepts unlimited Set-Cookie header fields with no size restrictions. Attackers can return many large cookies from a malicious server, causing Guzzle to store excessive data in memory and generate oversized Cookie headers that fail in handlers or destination servers.

Description from the CVE record, published by VulnCheck (the CVE Numbering Authority), via the NVD entry for CVE-2026-67353. Advisory title: “Guzzle: Unbounded response cookies risk denial of service”.

References

GitHub advisory GHSA-f283-ghqc-fg79 github.com
Vulncheck security advisory www.vulncheck.com

Other guzzlehttp/guzzle advisories

high CVE-2026-69246: Guzzle: Noncanonical host can bypass host-based checks 2026-08-03
medium CVE-2026-69245: Guzzle: Noncanonical cookie domain keeps subdomain scope 2026-08-03
medium CVE-2026-67354: Guzzle: URI fragments disclosed in redirect Referer headers 2026-07-20
medium CVE-2026-67355: Guzzle: Host-only cookie scope is not preserved 2026-07-20
medium CVE-2026-59883: Guzzle: Cookie Disclosure and Injection via IP-Address Domains 2026-07-20
medium CVE-2026-67339: Guzzle: Proxy-Authorization headers can be sent to origin servers 2026-07-20

Need help patching or upgrading? Laskyr does PHP and Laravel security fixes and upgrades. Tell us what you run and we reply with a plan and a price.

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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.