---
c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
SPDX-License-Identifier: curl
Title: CURLOPT_SSL_OPTIONS
Section: 3
Source: libcurl
See-also:
  - CURLOPT_PROXY_SSL_OPTIONS (3)
  - CURLOPT_SSLVERSION (3)
  - CURLOPT_SSL_CIPHER_LIST (3)
Protocol:
  - TLS
TLS-backend:
  - All
Added-in: 7.25.0
---

# NAME

CURLOPT_SSL_OPTIONS - SSL behavior options

# SYNOPSIS

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

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

# DESCRIPTION

Pass a long with a bitmask to tell libcurl about specific SSL
behaviors. Available bits:

## CURLSSLOPT_ALLOW_BEAST

Tells libcurl to not attempt to use any workarounds for a security flaw in the
SSL3 and TLS1.0 protocols. If this option is not used or this bit is set to 0,
the SSL layer libcurl uses may use a workaround for this flaw although it
might cause interoperability problems with some (older) SSL implementations.

**WARNING:** avoiding this workaround lessens the security, and by setting
this option to 1 you ask 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 such behavior is present. This option is only supported for Schannel
(the native Windows SSL library), with an 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 (BoringSSL, LibreSSL, 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 are searched in addition to the
native CA store.

Works with wolfSSL on Windows, Linux (Debian, Fedora, Gentoo, RHEL, Ubuntu),
macOS, Android and iOS (added in 8.3.0); with GnuTLS (added in 8.5.0) and with
OpenSSL and its forks (BoringSSL, LibreSSL, 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, OpenSSL, quictls and wolfSSL (but not AWS-LC or
BoringSSL). 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 OpenSSL, quictls and wolfSSL)

# DEFAULT

0

# %PROTOCOLS%

# EXAMPLE

~~~c
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);
  }
}
~~~

# 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).

# %AVAILABILITY%

# 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).
