Hi,
On 26-09-18 14:01, Arne Schwabe wrote:
> In my tests an OpenSSL 1.1.1 server does not accept TLS 1.0 only clients
> anymore. Unfortunately, Debian 8 still has OpenVPN 2.3.4, which is
> TLS 1.0 only without setting tls-version-min.
>
> We currently log only
> OpenSSL: error:14209102:SSL
> routines:tls_early_post_process_client_hello:unsupported protocol
> which indicates the right technical error but is not very helpful to a
> person without deep knowledge in SSL/TLS and OpenVPN's TLS version
> history.
>
> This commit adds a hopefully helpful message and also tells users how
> to fix the old Debian 8 clients. The error message will be displayed on
> the server side only.
>
> Note that connecting with an OpenSSL 1.1.1 client to a TLS 1.0 only
> server works fine.
>
> This behaviour is also not specific to OpenVPN. Using an openssl s_client
> with the -tls1 option against an openssl s_server exhibits the same
> behaviour.
>
> Patch V2: fixed message grammar, use tls-version-min 1.0 and clarify
> 2.3.6 and older to be actually between 2.3.2 and 2.3.6
> ---
> src/openvpn/crypto_openssl.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/src/openvpn/crypto_openssl.c b/src/openvpn/crypto_openssl.c
> index 9ec2048d..43d75b89 100644
> --- a/src/openvpn/crypto_openssl.c
> +++ b/src/openvpn/crypto_openssl.c
> @@ -199,7 +199,16 @@ crypto_print_openssl_errors(const unsigned int flags)
> "in common with the client. Your --tls-cipher setting might
> be "
> "too restrictive.");
> }
> -
> + else if (ERR_GET_REASON(err) == SSL_R_UNSUPPORTED_PROTOCOL)
> + {
> + msg(D_CRYPT_ERRORS, "TLS error: Unsupported protocol. This
> typically "
> + "indicates that client and server have no common TLS
> version enabled. "
> + "This can be caused by mismatched tls-version-min and
> tls-version-max "
> + "options on client and server. "
> + "If your OpenVPN client is between v2.3.6 and v2.3.2 try
> adding "
> + "tls-version-min 1.0 to the client configuration to use TLS
> 1.0+ "
> + "instead of TLS 1.0 only");
> + }
> msg(flags, "OpenSSL: %s", ERR_error_string(err, NULL));
> }
> }
>
Helpful message, patch looks good and passes the test suite. I didn't
manually test connecting with a tls 1.0-only client, but trust that you
have.
Acked-by: Steffan Karger <steffan.kar...@fox-it.com>
-Steffan
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