curl and libcurl before 7.50.1 do not check the client certificate when choosing the TLS connection to reuse, which might allow remote attackers to hijack the authentication of the connection by leveraging a previously created connection with a different client certificate.

curl and libcurl before 7.50.1 do not prevent TLS session resumption when the client certificate has changed, which allows remote attackers to bypass intended restrictions by resuming a session.

The default configuration for cURL and libcurl before 7.42.1 sends custom HTTP headers to both the proxy and destination server, which might allow remote proxy servers to obtain sensitive information by reading the header contents.