CURLOPT_SSL_OPTIONS(3) Library Functions Manual CURLOPT_SSL_OPTIONS(3)
NAME
CURLOPT_SSL_OPTIONS - SSL behavior options
SYNOPSIS
#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 work-around for this flaw although it 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 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. (Added in 7.44.0)
CURLSSLOPT_NO_PARTIALCHAIN
Tells libcurl to not accept "partial" certificate chains, which
it otherwise does by default. This option is only supported for
OpenSSL and fails the certificate verification if the chain ends
with an intermediate certificate and not with a root cert.
(Added in 7.68.0)
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, 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 wasn't 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 res;
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
/* weaken TLS only for use with silly servers */
curl_easy_setopt(curl, CURLOPT_SSL_OPTIONS, (long)CURLSSLOPT_ALLOW_BEAST |
CURLSSLOPT_NO_REVOKE);
res = curl_easy_perform(curl);
curl_easy_cleanup(curl);
}
}
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
CURLOPT_PROXY_SSL_OPTIONS(3), CURLOPT_SSLVERSION(3),
CURLOPT_SSL_CIPHER_LIST(3)
libcurl 2025-04-16 CURLOPT_SSL_OPTIONS(3)
curl 8.13.0 - Generated Wed May 7 16:27:01 CDT 2025