1--- 2c: Copyright (C) Daniel Stenberg, <daniel.se>, et al. 3SPDX-License-Identifier: curl 4Title: CURLOPT_SSL_VERIFYHOST 5Section: 3 6Source: libcurl 7See-also: 8 - CURLOPT_CAINFO (3) 9 - CURLOPT_PINNEDPUBLICKEY (3) 10 - CURLOPT_SSL_VERIFYPEER (3) 11--- 12 13# NAME 14 15CURLOPT_SSL_VERIFYHOST - verify the certificate's name against host 16 17# SYNOPSIS 18 19~~~c 20#include <curl/curl.h> 21 22CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_VERIFYHOST, long verify); 23~~~ 24 25# DESCRIPTION 26 27Pass a long as parameter specifying what to *verify*. 28 29This option determines whether libcurl verifies that the server cert is for 30the server it is known as. 31 32When negotiating TLS and SSL connections, the server sends a certificate 33indicating its identity. 34 35When CURLOPT_SSL_VERIFYHOST(3) is 2, that certificate must indicate that 36the server is the server to which you meant to connect, or the connection 37fails. Simply put, it means it has to have the same name in the certificate as 38is in the URL you operate against. 39 40Curl considers the server the intended one when the Common Name field or a 41Subject Alternate Name field in the certificate matches the hostname in the 42URL to which you told Curl to connect. 43 44If *verify* value is set to 1: 45 46In 7.28.0 and earlier: treated as a debug option of some sorts, not supported 47anymore due to frequently leading to programmer mistakes. 48 49From 7.28.1 to 7.65.3: setting it to 1 made curl_easy_setopt(3) return 50an error and leaving the flag untouched. 51 52From 7.66.0: treats 1 and 2 the same. 53 54When the *verify* value is 0, the connection succeeds regardless of the 55names in the certificate. Use that ability with caution! 56 57The default value for this option is 2. 58 59This option controls checking the server's certificate's claimed identity. 60The server could be lying. To control lying, see CURLOPT_SSL_VERIFYPEER(3). 61 62WARNING: disabling verification of the certificate allows bad guys to 63man-in-the-middle the communication without you knowing it. Disabling 64verification makes the communication insecure. Just having encryption on a 65transfer is not enough as you cannot be sure that you are communicating with 66the correct end-point. 67 68When libcurl uses secure protocols it trusts responses and allows for example 69HSTS and Alt-Svc information to be stored and used subsequently. Disabling 70certificate verification can make libcurl trust and use such information from 71malicious servers. 72 73# LIMITATIONS 74 75Secure Transport: If *verify* value is 0, then SNI is also disabled. SNI is 76a TLS extension that sends the hostname to the server. The server may use that 77information to do such things as sending back a specific certificate for the 78hostname, or forwarding the request to a specific origin server. Some hostnames 79may be inaccessible if SNI is not sent. 80 81# DEFAULT 82 832 84 85# PROTOCOLS 86 87All TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc. 88 89# EXAMPLE 90 91~~~c 92int main(void) 93{ 94 CURL *curl = curl_easy_init(); 95 if(curl) { 96 curl_easy_setopt(curl, CURLOPT_URL, "https://example.com"); 97 98 /* Set the default value: strict name check please */ 99 curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 2L); 100 101 curl_easy_perform(curl); 102 } 103} 104~~~ 105 106# AVAILABILITY 107 108If built TLS enabled. 109 110# RETURN VALUE 111 112Returns CURLE_OK if TLS is supported, and CURLE_UNKNOWN_OPTION if not. 113 114If 1 is set as argument, *CURLE_BAD_FUNCTION_ARGUMENT* is returned. 115