CVE-2026-55568: Guzzle is an extensible PHP HTTP client. Prior to 7.12.1, in certain configurations, traffic expected to be protected by TLS on the hop to the proxy i...

Description

Guzzle is an extensible PHP HTTP client. Prior to 7.12.1, in certain configurations, traffic expected to be protected by TLS on the hop to the proxy is transmitted in cleartext. Proxy authentication credentials (the Proxy-Authorization header, proxy userinfo in the proxy URL, or CURLOPT_PROXYUSERPWD) are sent without encryption, and the CONNECT target host and port for tunneled HTTPS requests are exposed. 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. 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. An application is affected when it sends requests through one of the built-in cURL handlers, configures an https:// proxy expecting the proxy connection itself to be encrypted, and runs with libcurl older than 7.50.2. This vulnerability is fixed in 7.12.1.

Metrics

CVSS 3.1

5.9/10

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

EPSS Probability

0.11%

1.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Guzzlephp	Guzzle	< 7.12.1

References

https://github.com/guzzle/guzzle/security/advisories/GHSA-wpwq-4j6v-78m3Third Party Advisory

Timeline

Published: Jun 23, 2026
Last Modified: Jun 26, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-55568?

Guzzle is an extensible PHP HTTP client. Prior to 7.12.1, in certain configurations, traffic expected to be protected by TLS on the hop to the proxy is transmitted in cleartext. Proxy authentication credentials (the Proxy-Authorization header, proxy userinfo in the proxy URL, or CURLOPT_PROXYUSERPWD) are sent without encryption, and the CONNECT target host and port for tunneled HTTPS requests are exposed. 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. 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. An application is affected when it sends requests through one of the built-in cURL handlers, configures an https:// proxy expecting the proxy connection itself to be encrypted, and runs with libcurl older than 7.50.2. This vulnerability is fixed in 7.12.1.

How severe is CVE-2026-55568?

CVE-2026-55568 has a CVSS score of 5.9/10 (MEDIUM severity). The EPSS model estimates a 0.11% probability of exploitation in the next 30 days.

How do I fix CVE-2026-55568?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.