115 lines
3.3 KiB
Markdown
115 lines
3.3 KiB
Markdown
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---
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c: Copyright (C) Daniel Stenberg, <daniel.se>, et al.
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SPDX-License-Identifier: curl
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Title: CURLOPT_SSL_VERIFYHOST
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Section: 3
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Source: libcurl
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See-also:
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- CURLOPT_CAINFO (3)
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- CURLOPT_PINNEDPUBLICKEY (3)
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- CURLOPT_SSL_VERIFYPEER (3)
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---
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# NAME
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CURLOPT_SSL_VERIFYHOST - verify the certificate's name against host
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# SYNOPSIS
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~~~c
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#include <curl/curl.h>
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CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_VERIFYHOST, long verify);
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~~~
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# DESCRIPTION
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Pass a long as parameter specifying what to *verify*.
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This option determines whether libcurl verifies that the server cert is for
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the server it is known as.
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When negotiating TLS and SSL connections, the server sends a certificate
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indicating its identity.
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When CURLOPT_SSL_VERIFYHOST(3) is 2, that certificate must indicate that
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the server is the server to which you meant to connect, or the connection
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fails. Simply put, it means it has to have the same name in the certificate as
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is in the URL you operate against.
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Curl considers the server the intended one when the Common Name field or a
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Subject Alternate Name field in the certificate matches the hostname in the
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URL to which you told Curl to connect.
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If *verify* value is set to 1:
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In 7.28.0 and earlier: treated as a debug option of some sorts, not supported
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anymore due to frequently leading to programmer mistakes.
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From 7.28.1 to 7.65.3: setting it to 1 made curl_easy_setopt(3) return
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an error and leaving the flag untouched.
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From 7.66.0: treats 1 and 2 the same.
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When the *verify* value is 0, the connection succeeds regardless of the
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names in the certificate. Use that ability with caution!
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The default value for this option is 2.
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This option controls checking the server's certificate's claimed identity.
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The server could be lying. To control lying, see CURLOPT_SSL_VERIFYPEER(3).
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WARNING: disabling verification of the certificate allows bad guys to
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man-in-the-middle the communication without you knowing it. Disabling
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verification makes the communication insecure. Just having encryption on a
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transfer is not enough as you cannot be sure that you are communicating with
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the correct end-point.
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When libcurl uses secure protocols it trusts responses and allows for example
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HSTS and Alt-Svc information to be stored and used subsequently. Disabling
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certificate verification can make libcurl trust and use such information from
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malicious servers.
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# LIMITATIONS
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Secure Transport: If *verify* value is 0, then SNI is also disabled. SNI is
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a TLS extension that sends the hostname to the server. The server may use that
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information to do such things as sending back a specific certificate for the
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hostname, or forwarding the request to a specific origin server. Some hostnames
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may be inaccessible if SNI is not sent.
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# DEFAULT
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2
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# PROTOCOLS
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All TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.
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# EXAMPLE
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~~~c
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int main(void)
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{
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CURL *curl = curl_easy_init();
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if(curl) {
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curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
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/* Set the default value: strict name check please */
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curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 2L);
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curl_easy_perform(curl);
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}
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}
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~~~
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# AVAILABILITY
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If built TLS enabled.
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# RETURN VALUE
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Returns CURLE_OK if TLS is supported, and CURLE_UNKNOWN_OPTION if not.
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If 1 is set as argument, *CURLE_BAD_FUNCTION_ARGUMENT* is returned.
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