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CURLOPT_SSL_VERIFYHOST(3)           libcurl          CURLOPT_SSL_VERIFYHOST(3)


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() 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.

       NSS: If CURLOPT_SSL_VERIFYPEER(3) is zero, CURLOPT_SSL_VERIFYHOST(3) is
       also set to zero and cannot be overridden.


DEFAULT

       2


PROTOCOLS

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


EXAMPLE

       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_SSL_VERIFYPEER(3), CURLOPT_CAINFO(3),

ibcurl 8.1.2                    April 26, 2023       CURLOPT_SSL_VERIFYHOST(3)

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