NAME

CURLOPT_SSLVERSION - preferred TLS/SSL version

SYNOPSIS

#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSLVERSION, long version);

DESCRIPTION

Pass a long as parameter to control which version range of SSL/TLS versions to use.

The SSL and TLS versions have typically developed from the most insecure version to be more and more secure in this order through history: SSL v2, SSLv3, TLS v1.0, TLS v1.1, TLS v1.2 and the most recent TLS v1.3.

Use one of the available defines for this purpose. The available options are:

CURL_SSLVERSION_DEFAULT: The default acceptable version range. The minimum acceptable version is by default TLS v1.0 since 7.39.0 (unless the TLS library has a stricter rule).
CURL_SSLVERSION_TLSv1: TLS v1.0 or later
CURL_SSLVERSION_SSLv2: SSL v2 - refused
CURL_SSLVERSION_SSLv3: SSL v3 - refused
CURL_SSLVERSION_TLSv1_0: TLS v1.0 or later (Added in 7.34.0)
CURL_SSLVERSION_TLSv1_1: TLS v1.1 or later (Added in 7.34.0)
CURL_SSLVERSION_TLSv1_2: TLS v1.2 or later (Added in 7.34.0)
CURL_SSLVERSION_TLSv1_3: TLS v1.3 or later (Added in 7.52.0)

The maximum TLS version can be set by using one of the CURL_SSLVERSION_MAX_ macros below. It is also possible to OR one of the CURL_SSLVERSION_ macros with one of the CURL_SSLVERSION_MAX_ macros.

CURL_SSLVERSION_MAX_DEFAULT: The flag defines the maximum supported TLS version by libcurl, or the default value from the SSL library is used. libcurl uses a sensible default maximum, which was TLS v1.2 up to before 7.61.0 and is TLS v1.3 since then - assuming the TLS library support it. (Added in 7.54.0)
CURL_SSLVERSION_MAX_TLSv1_0: The flag defines maximum supported TLS version as TLS v1.0. (Added in 7.54.0)
CURL_SSLVERSION_MAX_TLSv1_1: The flag defines maximum supported TLS version as TLS v1.1. (Added in 7.54.0)
CURL_SSLVERSION_MAX_TLSv1_2: The flag defines maximum supported TLS version as TLS v1.2. (Added in 7.54.0)
CURL_SSLVERSION_MAX_TLSv1_3: The flag defines maximum supported TLS version as TLS v1.3. (Added in 7.54.0)

In versions of curl prior to 7.54 the CURL_SSLVERSION_TLS options were documented to allow only the specified TLS version, but behavior was inconsistent depending on the TLS library.

DEFAULT

CURL_SSLVERSION_DEFAULT

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) {
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
    /* ask libcurl to use TLS version 1.0 or later */
    curl_easy_setopt(curl, CURLOPT_SSLVERSION, (long)CURL_SSLVERSION_TLSv1);
    /* Perform the request */
    curl_easy_perform(curl);
  }
}

HISTORY

SSLv2 is disabled by default since 7.18.1. Other SSL versions availability may vary depending on which backend libcurl has been built to use.

SSLv3 is disabled by default since 7.39.0.

SSLv2 and SSLv3 are refused completely since curl 7.77.0

Since 8.10.0 wolfSSL is fully supported. Before 8.10.0 the MAX macros were not supported with wolfSSL and the other macros did not set a minimum, but restricted the TLS version to only the specified one.

Rustls support added in 8.10.0.

AVAILABILITY

Added in curl 7.1

RETURN VALUE

Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.