Mismatch between renegotiation reported vs functional

[Matt Caswell]

On 25/03/2021 21:59, Shaun Robbins wrote:
> While trying to disable renegotiation the response from openssl reads 
> "Secure Renegotiation IS supported" even though renegotiation is failing.

Up until 2009 we just had "Renegotiation" as a concept. Then along came 
a man-in-the-middle attack on such renegotiation. For example see:

https://blog.qualys.com/product-tech/2009/11/05/ssl-and-tls-authentication-gap-vulnerability-discovered

The problem was a fundamental flaw in the design of renegotiation. So 
then RFC5746 was written in order to address this problem. 
Clients/Servers that support RFC5746 are said to support "Secure 
Renegotiation".

Support for secure renegotiation can be indicated via the use of a 
special ciphersuite, or through the use of extensions.

The "Secure Renegotiation IS supported" message means that both peers 
have indicated support for RFC5746. This is entirely independent of 
whether a server will actually *allow* any renegotiation at all. In fact 
it is impossible for the client to know this. The server does not 
indicate it in any way.

So the problem here is a misunderstanding about what this message 
*means*, i.e. it means both peers have indicated support for RFC5746 
(known as "secure renegotiation"). It doesn't tell you whether 
renegotiation will actually work.

Matt


> 
> OpenSSL Config:
> SSL_set_options(ssl_conn, SSL_OP_NO_RENEGOTIATION);
> 
> 
> ] $openssl s_client -connect localhost:443 -tls1_2
> [SNIP]
> New, TLSv1.2, Cipher is ECDHE-RSA-AES256-GCM-SHA384
> Server public key is 2048 bit
> *Secure Renegotiation IS supported
> *Compression: NONE
> Expansion: NONE
> No ALPN negotiated
> SSL-Session:
> [SNIP]
> ---
> HEAD / HTTP/1.1
> R
> RENEGOTIATING
> 139845827855680:error:14094153:SSL routines:ssl3_read_bytes:no 
> renegotiation:../ssl/record/rec_layer_s3.c:1560:
> 
> This article refers to this same problem with some screen shots under 
> section "Eliminating a false positive":
> 
> https://www.mcafee.com/blogs/enterprise/tips-securing-ssl-renegotiation/ 
> <https://www.mcafee.com/blogs/enterprise/tips-securing-ssl-renegotiation/>
> 
> Thanks!
> --
> Shaun Robbins