draconisplusplus/subprojects/curl-8.10.1/docs/libcurl/opts/CURLOPT_SSL_VERIFYHOST.md

---
c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
SPDX-License-Identifier: curl
Title: CURLOPT_SSL_VERIFYHOST
Section: 3
Source: libcurl
See-also:
  - CURLOPT_CAINFO (3)
  - CURLOPT_PINNEDPUBLICKEY (3)
  - CURLOPT_SSL_VERIFYPEER (3)
Protocol:
  - TLS
TLS-backend:
  - All
Added-in: 7.8.1
---

# NAME

CURLOPT_SSL_VERIFYHOST - verify the certificate's name against host

# SYNOPSIS

~~~c
#include <curl/curl.h>

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

# DESCRIPTION

Pass a long set to 2L to make libcurl verify the host in the server's TLS
certificate.

When negotiating a TLS connection, the server sends a certificate indicating
its identity.

When CURLOPT_SSL_VERIFYHOST(3) is set to 1 or 2, the server certificate must
indicate that it was made for the hostname or address curl connects to, or the
connection fails. Simply put, it means it has to have the same name in the
certificate as is used 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 hostname in the
URL to which you told curl to connect.

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

This option controls checking the server's certificate's claimed identity. The
separate CURLOPT_SSL_VERIFYPEER(3) options enables/disables verification that
the certificate is signed by a trusted Certificate Authority.

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.

# MATCHING

A certificate can have the name as a wildcard. The only asterisk (`*`) must
then be the left-most character and it must be followed by a period. The
wildcard must further contain more than one period as it cannot be set for a
top-level domain.

A certificate can be set for a numerical IP address (IPv4 or IPv6), but then
it should be a Subject Alternate Name kind and its type should correctly
identify the field as an IP address.

# 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%

# EXAMPLE

~~~c
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%

# HISTORY

In 7.28.0 and earlier: the value 1 was 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: libcurl treats 1 and 2 to this option the same.

# RETURN VALUE

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