CURLOPT_SSL_OPTIONS(3) Introduction to Library Functions
CURLOPT_SSL_OPTIONS - SSL behavior options
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_OPTIONS, long bitmask);
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.
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 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 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)
0
This functionality affects all TLS based protocols: HTTPS, FTPS,
IMAPS, POP3S, SMTPS etc.
All TLS backends support this option.
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);
}
}
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).
Added in curl 7.25.0
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).
CURLOPT_PROXY_SSL_OPTIONS(3), CURLOPT_SSLVERSION(3),
CURLOPT_SSL_CIPHER_LIST(3)
libcurl 2026-01-08 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.
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 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 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);
}
}
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
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 2026-01-08 CURLOPT_SSL_OPTIONS(3)