The darwinssl_connect_step1 function in lib/vtls/curl_darwinssl.c in
libcurl 7.31.0 through 7.39.0, when using the DarwinSSL (aka
SecureTransport) back-end for TLS, does not check if a cached TLS session
validated the certificate when reusing the session, which allows
man-in-the-middle attackers to spoof servers via a crafted certificate.