CURL-CVE-2013-6422

cert name check ignore with GnuTLS

(This issue is almost identical to the one named [CVE-2013-4545](CVE-2013-4545.html), but this problem affects a different SSL backend.) libcurl is vulnerable to a case of missing out the checking of the certificate `CN` or `SAN` name field when the digital signature verification is turned off. libcurl offers two separate and independent options for verifying a server's TLS certificate. `CURLOPT_SSL_VERIFYPEER` and `CURLOPT_SSL_VERIFYHOST`. The first one tells libcurl to verify the trust chain using a CA cert bundle, while the second tells libcurl to make sure that the name fields in the server certificate meets the criteria. Both options are enabled by default. This flaw had the effect that when an application disabled `CURLOPT_SSL_VERIFYPEER`, libcurl mistakenly also skipped the `CURLOPT_SSL_VERIFYHOST` check. Applications can disable `CURLOPT_SSL_VERIFYPEER` and still achieve security by doing the check on its own using other means. The curl command line tool is not affected by this problem as it either enables both options or disables both at the same time.