1---
2c: Copyright (C) Daniel Stenberg, <daniel@haxx.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)
11Protocol:
12  - TLS
13TLS-backend:
14  - All
15---
16
17# NAME
18
19CURLOPT_SSL_VERIFYHOST - verify the certificate's name against host
20
21# SYNOPSIS
22
23~~~c
24#include <curl/curl.h>
25
26CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_VERIFYHOST, long verify);
27~~~
28
29# DESCRIPTION
30
31Pass a long as parameter specifying what to *verify*.
32
33This option determines whether libcurl verifies that the server cert is for
34the server it is known as.
35
36When negotiating TLS and SSL connections, the server sends a certificate
37indicating its identity.
38
39When CURLOPT_SSL_VERIFYHOST(3) is 2, that certificate must indicate that
40the server is the server to which you meant to connect, or the connection
41fails. Simply put, it means it has to have the same name in the certificate as
42is in the URL you operate against.
43
44Curl considers the server the intended one when the Common Name field or a
45Subject Alternate Name field in the certificate matches the hostname in the
46URL to which you told Curl to connect.
47
48If *verify* value is set to 1:
49
50In 7.28.0 and earlier: treated as a debug option of some sorts, not supported
51anymore due to frequently leading to programmer mistakes.
52
53From 7.28.1 to 7.65.3: setting it to 1 made curl_easy_setopt(3) return
54an error and leaving the flag untouched.
55
56From 7.66.0: treats 1 and 2 the same.
57
58When the *verify* value is 0, the connection succeeds regardless of the
59names in the certificate. Use that ability with caution!
60
61The default value for this option is 2.
62
63This option controls checking the server's certificate's claimed identity.
64The server could be lying. To control lying, see CURLOPT_SSL_VERIFYPEER(3).
65
66WARNING: disabling verification of the certificate allows bad guys to
67man-in-the-middle the communication without you knowing it. Disabling
68verification makes the communication insecure. Just having encryption on a
69transfer is not enough as you cannot be sure that you are communicating with
70the correct end-point.
71
72When libcurl uses secure protocols it trusts responses and allows for example
73HSTS and Alt-Svc information to be stored and used subsequently. Disabling
74certificate verification can make libcurl trust and use such information from
75malicious servers.
76
77# LIMITATIONS
78
79Secure Transport: If *verify* value is 0, then SNI is also disabled. SNI is
80a TLS extension that sends the hostname to the server. The server may use that
81information to do such things as sending back a specific certificate for the
82hostname, or forwarding the request to a specific origin server. Some hostnames
83may be inaccessible if SNI is not sent.
84
85# DEFAULT
86
872
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