noble (3) CURLOPT_SSL_VERIFYHOST.3.gz

NAME

       CURLOPT_SSL_VERIFYHOST - verify the certificate's name against host

SYNOPSIS

       #include <curl/curl.h>

       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_VERIFYHOST, long verify);

DESCRIPTION

       Pass a long as parameter specifying what to verify.

       This option determines whether libcurl verifies that the server cert is for the server it is known as.

       When negotiating TLS and SSL connections, the server sends a certificate indicating its identity.

       When  CURLOPT_SSL_VERIFYHOST(3)  is  2,  that  certificate must indicate that the server is the server to
       which you meant to connect, or the connection fails. Simply put, it means it has to have the same name in
       the certificate as is in the URL you operate against.

       Curl  considers  the server the intended one when the Common Name field or a Subject Alternate Name field
       in the certificate matches the host name in the URL to which you told Curl to connect.

       If verify value is set to 1:

       In 7.28.0 and earlier: treated as a debug option of some sorts, not supported anymore due  to  frequently
       leading to programmer mistakes.

       From  7.28.1  to  7.65.3:  setting  it to 1 made curl_easy_setopt(3) return an error and leaving the flag
       untouched.

       From 7.66.0: treats 1 and 2 the same.

       When the verify value is 0, the connection succeeds regardless of the names in the certificate. Use  that
       ability with caution!

       The default value for this option is 2.

       This  option  controls  checking the server's certificate's claimed identity.  The server could be lying.
       To control lying, see CURLOPT_SSL_VERIFYPEER(3).

       WARNING: disabling verification of the certificate allows bad guys to man-in-the-middle the communication
       without  you  knowing it. Disabling verification makes the communication insecure. Just having encryption
       on a transfer is not enough as you cannot be sure that you are communicating with the correct end-point.

       When libcurl uses secure  protocols  it  trusts  responses  and  allows  for  example  HSTS  and  Alt-Svc
       information to be stored and used subsequently. Disabling certificate verification can make libcurl trust
       and use such information from malicious servers.

LIMITATIONS

       Secure Transport: If verify value is 0, then SNI is also disabled. SNI is a TLS extension that sends  the
       hostname  to the server. The server may use that information to do such things as sending back a specific
       certificate for the hostname, or forwarding the request to a specific origin server. Some  hostnames  may
       be inaccessible if SNI is not sent.

DEFAULT

       2

PROTOCOLS

       All TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.

EXAMPLE

       int main(void)
       {
         CURL *curl = curl_easy_init();
         if(curl) {
           curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");

           /* Set the default value: strict name check please */
           curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 2L);

           curl_easy_perform(curl);
         }
       }

AVAILABILITY

       If built TLS enabled.

RETURN VALUE

       Returns CURLE_OK if TLS is supported, and CURLE_UNKNOWN_OPTION if not.

       If 1 is set as argument, CURLE_BAD_FUNCTION_ARGUMENT is returned.

SEE ALSO

       CURLOPT_CAINFO(3), CURLOPT_PINNEDPUBLICKEY(3), CURLOPT_SSL_VERIFYPEER(3)