CVE-2026-55568 Guzzle: Silent HTTPS-Proxy Downgrade to Cleartext
Attackers can intercept cleartext proxy credentials and CONNECT targets when using older libcurl versions with HTTPS proxy configurations in Guzzle.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-55568?
CVE-2026-55568 is a medium-severity vulnerability in guzzle, published on 23 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-55568?
2 open source packages ship an affected version, including guzzlehttp/guzzle. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
guzzlehttp/guzzle Packagist | All versions | 7.12.1 |
guzzlehttp/guzzle Packagist | All versions | 7.12.1 |
Products include Guzzlephp Guzzle.
How do I fix CVE-2026-55568?
Upgrade guzzlehttp/guzzle to 7.12.1 or later.
Is CVE-2026-55568 being exploited?
There is no known exploitation of CVE-2026-55568 in the wild and no public exploit code.
Other vulnerabilities in guzzle
Sources
Also known as DEBIAN-CVE-2026-55568, GHSA-wpwq-4j6v-78m3, MINI-3mqr-qjrg-8jhq, MINI-873v-mgr7-c6xg, MINI-gqr9-3jwm-6j98, MINI-h2wg-xm94-jqrc and 6 more.