guzzlehttp/guzzle: Silent HTTPS-Proxy Downgrade to Cleartext

Exploitation

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

CVSS

5.9 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS

• CVE-2026-55568: 0.15% estimated exploitation activity in the next 30 days; percentile 4.00 (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 The built-in cURL handlers (GuzzleHttp\Handler\CurlHandler and GuzzleHttp\Handler\CurlMultiHandler, used by default whenever the PHP cURL extension is available) accept an https:// proxy — a proxy reached over a TLS-encrypted connection — through the proxy request option, client-level proxy defaults, or proxy environment variables such as httpproxy, httpsproxy, HTTPSPROXY, allproxy, and ALLPROXY. When the installed libcurl does not support HTTPS proxies, behavior depends on the libcurl version/build: - libcurl older than 7.50.2 silently treats an https:// proxy as a plaintext http:// proxy. The TLS connection to the proxy is never established, and the proxy leg is cleartext with no error or warning. - libcurl 7.50.2 through 7.51.x rejects the unsupported proxy scheme at connect time, so no cleartext exposure occurs, but the failure is late and opaque. - libcurl 7.52.0 or newer builds without HTTPS-proxy support also fail at connect time rather than downgrading. The…

Published by the source

19 Jun 2026, 14:17 UTC

Last modified by the source

19 Jun 2026, 14:18 UTC

Source last checked

26 Oct 2026, 14:49 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-wpwq-4j6v-78m3

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# Patch Next advisory brief: CVE-2026-55568

Advisory: guzzlehttp/guzzle: Silent HTTPS-Proxy Downgrade to Cleartext
IDs: CVE-2026-55568, GHSA-wpwq-4j6v-78m3
Record: https://patchnext.com/advisories/cve-2026-55568 (revision 1, source checked 26 Oct 2026, 14:49 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.9)
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-wpwq-4j6v-78m3 (GitHub-reviewed advisory GHSA-wpwq-4j6v-78m3 lists affected ranges: Packagist guzzlehttp/guzzle >=0 <7.12.1)

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