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Re: SSLv3 fallback attack POODLE

From: Kamil Dudka <kdudka_at_redhat.com>
Date: Wed, 15 Oct 2014 19:33:57 +0200

On Wednesday, October 15, 2014 17:26:53 Mark Adams wrote:
> Ray wrote:
> > What about enabling this by default when it's available, something
> > like if(!conn->data->set.ssl_disable_scsv)
> > SSL_CTX_set_mode(connssl->ctx, SSL_MODE_SEND_FALLBACK_SCSV), and
> > something could be put in CURLOPT_SSL_OPTIONS to allow the user disable
> > it like was done for BEAST, like CURLSSLOPT_ALLOW_DOWNGRADE_ATTACK would
> > set ssl_disable_scsv true.
>
> My understanding is that SSL_MODE_SEND_FALLBACK_SCSV should be set if and
> only if the TLS/SSL session being established is itself an attempt to
> establish a connection with a fallback TLS/SSL version following a previous
> handshake failure. It should not be set by default.
>
> Does libcurl currently attempt any fallback itself?

libcurl does implement a fallback to SSLv3 with NSS, at least. Ray's patch
disables it, which I believe is the right approach to take at this point.

Kamil

> If it just uses
> OpenSSL's own SSLv23_method, then I don't think there's an issue. In that
> case, I don't think it is possible for a man in the middle to force a
> fallback to SSL3. I'm sure someone will correct me if that's incorrect.
>
> Mark
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Received on 2014-10-15