2014-06-19 18:58:18 -04:00
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.\" **************************************************************************
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.\" * _ _ ____ _
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.\" * Project ___| | | | _ \| |
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.\" * / __| | | | |_) | |
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.\" * | (__| |_| | _ <| |___
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.\" * \___|\___/|_| \_\_____|
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.\" *
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2020-03-23 09:44:29 -04:00
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.\" * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
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2014-06-19 18:58:18 -04:00
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.\" *
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.\" * This software is licensed as described in the file COPYING, which
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.\" * you should have received as part of this distribution. The terms
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2016-02-02 18:19:02 -05:00
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.\" * are also available at https://curl.haxx.se/docs/copyright.html.
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2014-06-19 18:58:18 -04:00
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.\" *
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.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
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.\" * copies of the Software, and permit persons to whom the Software is
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.\" * furnished to do so, under the terms of the COPYING file.
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.\" *
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.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
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.\" * KIND, either express or implied.
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.\" *
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.\" **************************************************************************
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.\"
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.TH CURLOPT_SSL_OPTIONS 3 "19 Jun 2014" "libcurl 7.37.0" "curl_easy_setopt options"
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.SH NAME
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CURLOPT_SSL_OPTIONS \- set SSL behavior options
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.SH SYNOPSIS
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#include <curl/curl.h>
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CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_OPTIONS, long bitmask);
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.SH DESCRIPTION
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2019-12-02 04:55:33 -05:00
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Pass a long with a bitmask to tell libcurl about specific SSL
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behaviors. Available bits:
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.IP CURLSSLOPT_ALLOW_BEAST
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Tells libcurl to not attempt to use any workarounds for a security flaw in the
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SSL3 and TLS1.0 protocols. If this option isn't used or this bit is set to 0,
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the SSL layer libcurl uses may use a work-around for this flaw although it
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might cause interoperability problems with some (older) SSL
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implementations. WARNING: avoiding this work-around lessens the security, and
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by setting this option to 1 you ask for exactly that. This option is only
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supported for DarwinSSL, NSS and OpenSSL.
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.IP CURLSSLOPT_NO_REVOKE
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Tells libcurl to disable certificate revocation checks for those SSL backends
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where such behavior is present. This option is only supported for Schannel
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(the native Windows SSL library), with an exception in the case of Windows'
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Untrusted Publishers blacklist which it seems can't be bypassed. (Added in
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7.44.0)
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.IP CURLSSLOPT_NO_PARTIALCHAIN
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Tells libcurl to not accept "partial" certificate chains, which it otherwise
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does by default. This option is only supported for OpenSSL and will fail the
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certificate verification if the chain ends with an intermediate certificate
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and not with a root cert. (Added in 7.68.0)
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schannel: add "best effort" revocation check option
- Implement new option CURLSSLOPT_REVOKE_BEST_EFFORT and
--ssl-revoke-best-effort to allow a "best effort" revocation check.
A best effort revocation check ignores errors that the revocation check
was unable to take place. The reasoning is described in detail below and
discussed further in the PR.
---
When running e.g. with Fiddler, the schannel backend fails with an
unhelpful error message:
Unknown error (0x80092012) - The revocation function was unable
to check revocation for the certificate.
Sadly, many enterprise users who are stuck behind MITM proxies suffer
the very same problem.
This has been discussed in plenty of issues:
https://github.com/curl/curl/issues/3727,
https://github.com/curl/curl/issues/264, for example.
In the latter, a Microsoft Edge developer even made the case that the
common behavior is to ignore issues when a certificate has no recorded
distribution point for revocation lists, or when the server is offline.
This is also known as "best effort" strategy and addresses the Fiddler
issue.
Unfortunately, this strategy was not chosen as the default for schannel
(and is therefore a backend-specific behavior: OpenSSL seems to happily
ignore the offline servers and missing distribution points).
To maintain backward-compatibility, we therefore add a new flag
(`CURLSSLOPT_REVOKE_BEST_EFFORT`) and a new option
(`--ssl-revoke-best-effort`) to select the new behavior.
Due to the many related issues Git for Windows and GitHub Desktop, the
plan is to make this behavior the default in these software packages.
The test 2070 was added to verify this behavior, adapted from 310.
Based-on-work-by: georgeok <giorgos.n.oikonomou@gmail.com>
Co-authored-by: Markus Olsson <j.markus.olsson@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Closes https://github.com/curl/curl/pull/4981
2020-02-26 05:24:26 -05:00
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.IP CURLSSLOPT_REVOKE_BEST_EFFORT
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Tells libcurl to ignore certificate revocation checks in case of missing or
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offline distribution points for those SSL backends where such behavior is
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present. This option is only supported for Schannel (the native Windows SSL
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library). If combined with \fICURLSSLOPT_NO_REVOKE\fP, the latter takes
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precedence. (Added in 7.70.0)
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2014-06-19 18:58:18 -04:00
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.SH DEFAULT
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0
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.SH PROTOCOLS
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All TLS-based protocols
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.SH EXAMPLE
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2017-05-31 05:56:28 -04:00
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.nf
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CURL *curl = curl_easy_init();
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if(curl) {
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curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
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/* weaken TLS only for use with silly servers */
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curl_easy_setopt(curl, CURLOPT_SSL_OPTIONS, CURLSSLOPT_ALLOW_BEAST |
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CURLSSLOPT_NO_REVOKE);
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ret = curl_easy_perform(curl);
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curl_easy_cleanup(curl);
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}
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.fi
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2014-06-19 18:58:18 -04:00
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.SH AVAILABILITY
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Added in 7.25.0
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.SH RETURN VALUE
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Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
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.SH "SEE ALSO"
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.BR CURLOPT_SSLVERSION "(3), " CURLOPT_SSL_CIPHER_LIST "(3), "
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