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 workaround for this flaw although it might cause interoperability problems with some (older) SSL implementations. WARNING: avoiding this workaround lessens the security, and by set- ting 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 sup- ported for Schannel (the native Windows SSL library), with an excep- tion 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 verifi- cation 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_RE- VOKE, the latter takes precedence. (Added in 7.70.0) CURLSSLOPT_NATIVE_CA Tell libcurl to use the operating system's native CA store for cer- tificate verification. This option is independent of other CA cer- tificate 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 vi- olation 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 This functionality affects all TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc. only 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_CI- PHER_LIST(3) libcurl 2026-08-27 CURLOPT_SSL_OPTIONS(3)
NAME | SYNOPSIS | DESCRIPTION | DEFAULT | PROTOCOLS | EXAMPLE | HISTORY | AVAILABILITY | RETURN VALUE | SEE ALSO
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