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96 lines
3.7 KiB
Groff
96 lines
3.7 KiB
Groff
.\" generated by cd2nroff 0.1 from CURLOPT_SSL_VERIFYHOST.md
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.TH CURLOPT_SSL_VERIFYHOST 3 "2024-08-02" libcurl
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.SH NAME
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CURLOPT_SSL_VERIFYHOST \- verify the certificate\(aqs name against host
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.SH SYNOPSIS
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.nf
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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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.fi
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.SH DESCRIPTION
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Pass a long set to 2L to make libcurl verify the host in the server\(aqs TLS
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certificate.
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When negotiating a TLS connection, the server sends a certificate indicating
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its identity.
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When \fICURLOPT_SSL_VERIFYHOST(3)\fP is set to 1 or 2, the server certificate must
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indicate that it was made for the hostname or address curl connects to, or the
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connection fails. Simply put, it means it has to have the same name in the
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certificate as is used 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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When the \fIverify\fP value is 0, the connection succeeds regardless of the names
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in the certificate. Use that ability with caution,
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This option controls checking the server\(aqs certificate\(aqs claimed identity. The
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separate \fICURLOPT_SSL_VERIFYPEER(3)\fP options enables/disables verification that
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the certificate is signed by a trusted Certificate Authority.
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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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.SH MATCHING
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A certificate can have the name as a wildcard. The only asterisk (\fI*\fP) must
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then be the left\-most character and it must be followed by a period. The
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wildcard must further contain more than one period as it cannot be set for a
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top\-level domain.
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A certificate can be set for a numerical IP address (IPv4 or IPv6), but then
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it should be a Subject Alternate Name kind and its type should correctly
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identify the field as an IP address.
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.SH LIMITATIONS
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Secure Transport: If \fIverify\fP value is 0, then SNI is also disabled. SNI is a
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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
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hostnames may be inaccessible if SNI is not sent.
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.SH DEFAULT
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2
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.SH PROTOCOLS
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This functionality affects all TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.
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All TLS backends support this option.
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.SH EXAMPLE
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.nf
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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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.fi
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.SH AVAILABILITY
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Added in curl 7.8.1
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.SH HISTORY
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In 7.28.0 and earlier: the value 1 was treated as a debug option of some
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sorts, not supported 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 \fIcurl_easy_setopt(3)\fP return
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an error and leaving the flag untouched.
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From 7.66.0: libcurl treats 1 and 2 to this option the same.
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.SH RETURN VALUE
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Returns CURLE_OK if TLS is supported, and CURLE_UNKNOWN_OPTION if not.
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.SH SEE ALSO
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.BR CURLOPT_CAINFO (3),
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.BR CURLOPT_PINNEDPUBLICKEY (3),
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.BR CURLOPT_SSL_VERIFYPEER (3)
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