CURLOPT_SSL_OPTIONS(3)

📦
version 8.18.0 · 25 versions
, in fedora 44

💅 CURLOPT_SSL_OPTIONS ✨

ok so real talk, this is CURLOPT_SSL_OPTIONS from the libcurl fam — the manual name is literally just sitting right there in the title, bestie, you can't miss it. Today we're customizing how libcurl does its whole SSL vibe. 🎀

✨ SYNOPSIS ✨

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_OPTIONS, long bitmask);

🌸 DESCRIPTION 🌸

So you pass a long that's a bitmask (iykyk: a bunch of on/off switches crammed into one number 💅) and it tells libcurl exactly which SSL behaviors you want. Here's every bit, no cap, all of them:

  • CURLSSLOPT_ALLOW_BEAST — tells libcurl to not attempt any workarounds for a security flaw in the SSL3 and TLS1.0 protocols. If you don't use this option, or you set this bit to 0, the SSL layer libcurl's using may put a work-around in place for that flaw — which might cause interoperability problems with some (older) SSL implementations. ⚠️ WARNING: avoiding this work-around lessens the security, and by setting this option to 1 you are asking for exactly that. This option is only supported for Secure Transport and OpenSSL.
  • CURLSSLOPT_NO_REVOKE — tells libcurl to disable certificate revocation checks for those SSL backends where that behavior even exists. This option is only supported for Schannel (the native Windows SSL library), with one exception in the case of Windows' Untrusted Publishers block list, which it seems cannot be bypassed. 💀
  • CURLSSLOPT_NO_PARTIALCHAIN — tells libcurl to not accept "partial" certificate chains, which it otherwise does by default. This option fails the certificate verification if the chain ends with an intermediate certificate and not with a root cert. 🌈 Works with OpenSSL and its forks (LibreSSL, BoringSSL, etc). (Added in 7.68.0) Works with Schannel if the user specified certificates to verify the peer. (Added in 8.15.0)
  • CURLSSLOPT_REVOKE_BEST_EFFORT — tells libcurl to ignore certificate revocation checks in case of missing or offline distribution points, for those SSL backends where such behavior is present. This option is only supported for Schannel (the native Windows SSL library). If combined with CURLSSLOPT_NO_REVOKE, the latter takes precedence. (Added in 7.70.0)
  • CURLSSLOPT_NATIVE_CA — tell libcurl to use the operating system's native CA store for certificate verification. This option is independent of other CA certificate locations set at run time or build time — those locations get searched in addition to the native CA store. 🦋 Works with wolfSSL on Windows, Linux (Debian, Ubuntu, Gentoo, Fedora, RHEL), macOS, Android and iOS (added in 8.3.0); with GnuTLS (added in 8.5.0) and with OpenSSL and its forks (LibreSSL, BoringSSL, etc) on Windows (Added in 7.71.0). This works with Rustls on Windows, macOS, Android and iOS. On Linux it is equivalent to using the Mozilla CA certificate bundle. When used with Rustls only the native CA store is consulted, not other locations set at run time or build time. (Added in 8.13.0) 👑
  • CURLSSLOPT_AUTO_CLIENT_CERT — tell libcurl to automatically locate and use a client certificate for authentication, when requested by the server. This option is only supported for Schannel (the native Windows SSL library). Prior to 7.77.0 this was the default behavior in libcurl with Schannel. Since the server can request any certificate that supports client authentication in the OS certificate store, it could be a privacy violation and unexpected. 🙈 (Added in 7.77.0)
  • CURLSSLOPT_EARLYDATA — tell libcurl to try sending application data as TLS1.3 early data. This option is supported for GnuTLS, wolfSSL, quictls and OpenSSL (but not BoringSSL or AWS-LC). It works on TCP and QUIC connections using ngtcp2. This option works on a best effort basis — in cases when it was not possible to send early data, the request is resent normally post-handshake. This option does not work when using QUIC. (Added in 8.11.0 for GnuTLS and 8.13.0 for wolfSSL, quictls and OpenSSL) 🔥

🎀 DEFAULT 🎀

0

🧚 PROTOCOLS 🧚

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

All TLS backends support this option. 💖

⭐ EXAMPLE ⭐

int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode result;
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
    /* weaken TLS only for use with silly servers */
    curl_easy_setopt(curl, CURLOPT_SSL_OPTIONS,
                     CURLSSLOPT_ALLOW_BEAST | CURLSSLOPT_NO_REVOKE);
    result = curl_easy_perform(curl);
    curl_easy_cleanup(curl);
  }
}

like, yes, that comment is literally in there, "weaken TLS only for use with silly servers" — she said what she said 💀

🦋 HISTORY 🦋

CURLSSLOPT_* macros became long types in 8.15.0 — prior to this version a long cast was necessary when passed to curl_easy_setopt(3). glow-up fr fr ✨

💜 AVAILABILITY 💜

Added in curl 7.25.0

🫶 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). 😭

👑 SEE ALSO 👑

ok that's the whole page, mwah 💋 — this gem is from the libcurl manual, dated 2026-10-12, and yeah the header/footer both say CURLOPT_SSL_OPTIONS(3) because that's just her name, periodt. 🍓💅

📦 where this page comes from