guzzlehttp/guzzle: Dot-Only Cookie Domains Match All Hosts

Exploitation

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

CVSS

5.8 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N

EPSS

• CVE-2026-55767: 0.21% estimated exploitation activity in the next 30 days; percentile 11.44 (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.

Impact CookieJar incorrectly accepts cookies with a dot-only Domain attribute, such as Domain=., Domain=.., Domain=..., and whitespace-padded variants such as Domain= . . In affected versions, SetCookie::matchesDomain() removes leading dots from the cookie domain, normalizing dot-only values to the empty string; SetCookie::validate() only rejected a strictly empty domain, so these cookies could be stored and the empty normalized domain was treated as matching any request host. An attacker-controlled origin that an application requests with a shared cookie jar can therefore set a cookie that Guzzle later sends to unrelated hosts using the same jar. This may allow cookie injection or session fixation against downstream services, depending on how those services interpret the injected cookie. Applications are affected when they use Guzzle's cookie support, for example new Client(['cookies' = true]) or an explicit shared CookieJar, and reuse the same jar across attacker-controlled and…

Published by the source

19 Jun 2026, 14:37 UTC

Last modified by the source

5 Aug 2026, 21:49 UTC

Source last checked

26 Oct 2026, 14:50 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-cwxw-98qj-8qjx

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-55767

Advisory: guzzlehttp/guzzle: Dot-Only Cookie Domains Match All Hosts
IDs: CVE-2026-55767, GHSA-cwxw-98qj-8qjx
Record: https://patchnext.com/advisories/cve-2026-55767 (revision 1, source checked 26 Oct 2026, 14:50 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: guzzlehttp/guzzle 7.12.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist guzzlehttp/guzzle: affected < 7.12.1; fixed in 7.12.1

## Suggested inspection (read-only)
- Packagist guzzlehttp/guzzle: 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 guzzlehttp/guzzle.
- 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-cwxw-98qj-8qjx (GitHub-reviewed advisory GHSA-cwxw-98qj-8qjx lists affected ranges: Packagist guzzlehttp/guzzle >=0 <7.12.1)

Commands are suggestions: review each one before running it.