CVE-2026-55568
MediumCVSS 5.9Exploitation Probability (EPSS)
Low risk1th percentile — higher than 1% of all known CVEs
Summary
Vulnerability in Guzzle (PHP HTTP client) before 7.12.1 causes traffic expected to be TLS-protected to the proxy to be transmitted in cleartext under certain configurations. This occurs when using built-in cURL handlers (CurlHandler or CurlMultiHandler) with libcurl older than 7.50.2 and an https:// proxy URL — libcurl silently treats it as http://, never establishing an encrypted connection.
Risk Assessment
The risk for organizations is the exposure of proxy authentication credentials (Proxy-Authorization header, proxy userinfo in URL, or CURLOPT_PROXYUSERPWD) and the CONNECT target host and port for tunneled HTTPS requests, potentially allowing an attacker on the local network to intercept sensitive information.
Recommendation
Immediately update Guzzle to version 7.12.1 or later. Additionally, check the libcurl version in your production environment and consider upgrading it to at least 7.50.2 to prevent similar issues in the future.
Original NVD description (English source)
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.