[courier-users] TLS/SSL Client Renegotiation Attacks

[Brian A. Seklecki]

All:

A lot of projects(1) are analyzing how their specific protocol may
be specifically vulnerable due to the recently release TLS/SSL
protocol-level vulnerability(2) involving client re-negotiations.

With couriertcpd(8), does the SSL wrapper present the same
limitation for cleartext protocols like SMTP and IMAP?

Does the client or server SMTP code utilize renegotiations? I
would think not.

My understanding would be that, with SSL certificate exchange, other
than validating the identity of a client/server connection against
global PKI (Trusted CAs for signed mail server certificates), at
no point during a single SMTP or IMAP transaction would a new
certificate be presented for additional security credentials.

Of course, that doesn't mean the session cannot be hijacked for
data injection (Bypassing a relay restriction in ESTMPD, for
example)

SQWebmail sessions could be taken over, as well, I suppose.

FreeBSD has disabled renegotiation support at the library-level for the
in-tree OpenSSL. Apache has disabled renegotiation in the daemon code.

I'm curious what our approach will be.

1. OpenLDAP:
http://www.openldap.org/lists/ietf-ldapext/200911/msg00000.html
2. http://extendedsubset.com/?p=8

Thanks, ~BAS

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[Sam Varshavchik]

Brian A. Seklecki writes:

> All:
>
> A lot of projects(1) are analyzing how their specific protocol may
> be specifically vulnerable due to the recently release TLS/SSL
> protocol-level vulnerability(2) involving client re-negotiations.
>
> With couriertcpd(8), does the SSL wrapper present the same
> limitation for cleartext protocols like SMTP and IMAP?
>
> Does the client or server SMTP code utilize renegotiations? I
> would think not.

No. There is no support for renegotiation in the client or the server. The
client never requests a renegotiation. The server ignores renegotiation
requests, and never does a handshake after the connection is established.
Not actually quite sure what happens if the server gets a renegotation
request and ignores it. Either the session continues as is, or it breaks
with an error.