proto-default skips SSH verification

When a user invokes curl using a schemeless URL combined with --proto-default sftp or scp, a disconnect occurs between the tool layer and libcurl. The tool layer incorrectly infers the URL scheme, which erroneously bypasses the initialization of critical SSH security options like...

Native CA trust persist

libcurl keeps previously used connections in a connection pool for subsequent transfers to reuse if one of them matches the setup. An easy handle that first uses default native CA trust can continue trusting the native platform store after the application switches that same handle to custom CA...

HTTP/2 stream-dependency tree UAF

A use-after-free vulnerability exists in libcurl when an application configures an HTTP/2 stream-dependency tree via CURLOPTSTREAMDEPENDS or CURLOPTSTREAMDEPENDSE, subsequently invokes curleasyreset, and finally terminates the handle with curleasycleanup. During this final cleanup phase, libcurl...

sending old referer

A vulnerability in libcurl caused the HTTP Referer: header to persist even when explicitly cleared. While the documentation states that passing NULL to CURLOPTREFERER suppresses the header, the option failed to clear the internal state. As a result, the previous referrer string was erroneously...

UAF after pause in socket callback

Calling curleasypause within the event-based CURLMOPTSOCKETFUNCTION callback triggers a use-after-free vulnerability, where libcurl attempts to store a flag using a dangling struct pointer immediately after that pointer's memory has been freed...

stale proxy password leak

libcurl had a flaw that when instructed to clear proxy authentication credentials which made it not do so, leaving the old credentials around to get used for subsequent transfers that should not know nor use them...

PT-2026-51743

Name of the Vulnerable Software and Affected Versions libcurl affected versions not specified Description When performing a transfer to a specific HTTP origin hostA using Digest authentication and subsequently changing the origin to a different one hostB while reusing the same handle, libcurl...

PT-2026-51753

Name of the Vulnerable Software and Affected Versions libcurl affected versions not specified Description A use-after-free issue occurs when the curl easy pause function is called within the event-based CURLMOPT SOCKETFUNCTION callback. This leads to a situation where libcurl attempts to store a...

PT-2026-51756

Name of the Vulnerable Software and Affected Versions libcurl affected versions not specified Description Applications using libcurl for transfers via SCP:// or SFTP:// that utilize the CURLOPT SSH KEYFUNCTION callback may silently accept an untrusted server. This occurs when a server presents a...

PT-2026-51750

Name of the Vulnerable Software and Affected Versions libcurl affected versions not specified Description When reusing a handle for sequential transfers driven by environment-variable proxy configuration, the software fails to clear the proxy authentication state between requests. If an initial...

PT-2026-51752

Name of the Vulnerable Software and Affected Versions libcurl affected versions not specified Description A flaw exists where the software fails to clear proxy authentication credentials when instructed to do so. This results in old credentials remaining available and potentially being used for...

PT-2026-51754

Name of the Vulnerable Software and Affected Versions libcurl affected versions not specified Description An issue exists where libcurl may send request data on a new connection before enforcing certificate verification failure. This occurs when a user first connects to a legitimate HTTP/3 server...

PT-2026-51755

Name of the Vulnerable Software and Affected Versions libcurl affected versions not specified Description An issue exists where the HTTP Referer: header persists even after being explicitly cleared. Although passing NULL to CURLOPT REFERER is intended to suppress the header, the internal state 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 CURLOPTPROXYUSERPW...

CVE-2026-55568 Guzzle: Silent HTTPS-Proxy Downgrade to Cleartext

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 CURLOPTPROXYUSERPW...

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 CURLOPTPROXYUSERPW...

CVE-2026-55568

Summary (CVE-2026-55568) : Guzzle’s built‑in cURL handlers (CurlHandler/CurlMultiHandler) can downgrade an https:// proxy to plaintext when using libcurl older than 7.50.2, exposing proxy credentials and the CONNECT host/port. The issue occurs if an https proxy is configured and the app runs with...

GHSA-WPWQ-4J6V-78M3 guzzlehttp/guzzle: Silent HTTPS-Proxy Downgrade to Cleartext

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...

guzzlehttp/guzzle: Silent HTTPS-Proxy Downgrade to Cleartext

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...

Silent HTTPS proxy downgrade to cleartext

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...