Re: RFC 9266: Channel Bindings for TLS 1.3 support

On Thu, Nov 20, 2025 at 01:59:22PM -0800, Jacob Champion wrote:
> On Thu, Nov 20, 2025 at 1:52 PM Heikki Linnakangas <hlinnaka@iki.fi> wrote:
> > PostgreSQL does support channel binding, with tls-server-end-point. I
> > believe that sufficient to prevent an attack like that.
> 
> No, IIRC unique bindings (-unique and -exporter) prevent MITM even if
> the attacker has the server's private key, as long as they do not also
> possess the SCRAM verifiers. tls-server-end-point does not prevent
> against that (so you can terminate TLS on a different node from the
> verifiers).

If the attacker has the server's private keys then presumably also have
the credentials needed to also terminate the SASL/GSS-API mechanism's
server/acceptor side, so channel binding will not protect you.

The original intent for channel binding was so we could have channels
that authenticate end-points either very weakly (IPsec) or not at all
(TLS w/ anonymous ciphersuites, IPsec w/ BTNS).  But channel binding
also serves to detect unwanted proxies -- not wanted by the app, but
maybe wanted by the user.  Channel binding has also inspired various
token binding schemes to reduce the risk of bearer token compromise.

Nico
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