Bug 2491767 (CVE-2026-55568)

Summary: CVE-2026-55568 guzzlehttp/guzzle: Guzzle: Information disclosure via cleartext proxy communication
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Guzzle, an extensible PHP HTTP client. In certain configurations, when an application uses Guzzle's built-in cURL handlers with an HTTPS proxy and an older version of libcurl (prior to 7.50.2), traffic intended to be protected by TLS is transmitted in cleartext. This can lead to the disclosure of sensitive information, such as proxy authentication credentials and the target host and port for tunneled HTTPS requests, to an unencrypted proxy. A remote attacker could exploit this to intercept sensitive data.
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Bug Depends On: 2491788, 2491789, 2491791, 2491793    
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Description OSIDB Bzimport 2026-06-23 16:01:23 UTC 
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.