CURLOPT_SSL_VERIFYHOST(3)

📦
version 8.18.0 · 25 versions
, in fedora 44

💅 CURLOPT_SSL_VERIFYHOST 💅

okay bestie, grab a strawberry drink 🍓 because this one is literally about making sure the server you're talking to is actually who it says it is. this page lives in the Library Functions Manual, and it's a big ol' libcurl icon.

✨ NAME ✨

CURLOPT_SSL_VERIFYHOST — verify the certificate's name against host 🎀

🌸 SYNOPSIS 🌸

#include <curl/curl.h>

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

🦋 DESCRIPTION 🦋

So here's the vibe: you pass a long set to 2L and that tells libcurl "hey, please actually check the host in the server's TLS certificate, mkay?" 👑

When you're negotiating a TLS connection, the server sends over a certificate that's basically its ID card. it's giving "hi, this is me, here's proof."

When CURLOPT_SSL_VERIFYHOST(3) is set to 1 or 2, that server certificate must indicate that it was made for the hostname or address curl connects to — otherwise the connection just fails, periodt. Simply put: the name in the certificate has to be the same name that's in the URL you're operating against. no catfishing allowed 💀

curl considers the server to be the intended one when the Common Name field or a Subject Alternate Name field in the certificate matches the hostname in the URL you told curl to connect to.

When the verify value is 0, the connection succeeds regardless of the names in the certificate. yes, it just... doesn't care. use that ability with caution, fr fr 🙈

This option controls checking the server certificate's claimed identity. The separate CURLOPT_SSL_VERIFYPEER(3) option is the one that enables/disables verification that the certificate is signed by a trusted Certificate Authority. two different jobs, two different options, don't mix them up bestie 🫶

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, because you cannot be sure that you are communicating with the correct end-point. encryption to someone is not the same as encryption to the right someone 😭

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. so like, it's not just this one connection — it can poison the vibe going forward 💀

🧚 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, because it cannot be set for a top-level domain. no cap, them's the rules ⭐

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. so it's gotta be labelled properly, iykyk 🌈

💖 DEFAULT 💖

2

the good default. the correct default. we love to see it 👑

🔥 PROTOCOLS 🔥

This functionality affects all TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.

All TLS backends support this option. all of them. every single one. iconic 💅

🌟 EXAMPLE 🌟

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 🎀

Added in curl 7.8.1 — a certified vintage, honestly 🕰️

🐚 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 💜

curl_easy_setopt(3) returns a CURLcode indicating success or error.

CURLE_OK (0) means everything was OK, non-zero means an error occurred, see libcurl-errors(3). zero is the slay outcome, anything else means go read the errors page 😌

👑 SEE ALSO 👑

that's the whole page bestie, go verify some hosts 💖✨🦋

libcurl · 2026-10-12 · CURLOPT_SSL_VERIFYHOST(3) — mwah, stan this manpage, byeee 🫶🎀

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