DragonFly On-Line Manual Pages
CURLOPT_SSL_VERIFYHOST(3) libcurl CURLOPT_SSL_VERIFYHOST(3)
CURLOPT_SSL_VERIFYHOST - verify the certificate's name against host
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_VERIFYHOST, long verify);
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
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.
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.
All TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.
CURL *curl = curl_easy_init();
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);
If built TLS enabled.
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.
ibcurl 8.1.2 April 26, 2023 CURLOPT_SSL_VERIFYHOST(3)