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Date: Wed, 11 Aug 2021 10:31:58 -0500
From: Eric Blake <>
Subject: Re: STARTTLS vulnerabilities

On Wed, Aug 11, 2021 at 08:16:34AM +0200, Hanno Böck wrote:
> Of course it's a very obvious idea for further research to look if one
> finds similar vulnerabilities to the ones we found in other protocols.
> So I'd really like to encourage other people to look for this.
> FWIW there are a lot of protocols with a STARTTLS mechanism, here's the
> list of supported protocols by OpenSSL:
> 	smtp
> 	pop3
> 	imap
> 	ftp
> 	xmpp
> 	xmpp-server
> 	telnet
> 	irc
> 	mysql
> 	postgres
> 	lmtp
> 	nntp
> 	sieve
> 	ldap

Not mentioned in that list was ndb, but as far as I can tell, that
project has already documented the ramifications of opportunistic
encryption as being a security risk, and all known implementations
(both servers and clients) with TLS support have a mode of execution
that ensures the connection is dropped if a downgrade attack is

But I welcome review from those with more experience from the security
side of things.

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization: |

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