Re: STARTTLS & EHLO

[Alexey Melnikov <[e-mail]>]

Tony Finch wrote:

>On Mon, 26 Jan 2009, John C Klensin wrote:
>  
>
>>Right. The quoted 3207 text says to me that the server is
>>required discard the data sent earlier by the client as part of
>>EHLO.  I don't see any expectation that it be required to
>>discard the fact that EHLO was sent.
>>    
>>
>The quote is:
>                             The server MUST discard any knowledge
>   obtained from the client, such as the argument to the EHLO command,
>   which was not obtained from the TLS negotiation itself.  The client
>   MUST discard any knowledge obtained from the server, such as the list
>   of SMTP service extensions, which was not obtained from the TLS
>   negotiation itself.
>
>The argument to EHLO is just an example and is clearly not the entirety of
>what the server is supposed to discard.
>  
>
>>Indeed, unless there is something else in 3207, the client isn't
>>even required to discard the response from EHLO with the
>>server-supported feature list,
>>    
>>
>It is required to do so.
>  
>
Indeed. Before STARTTLS was negotiated there is no guaranty that a 
man-in-the-middle attacker hasn't modified the list of capabilities 
advertised by the server.