Hello Ralf, On Fri, Oct 24, 2014 at 10:03:47AM +0200, Ralf Jung wrote: > Something here cannot be quite right, or at least it's very misleading: > I use an IMAP accounts for an e-mail address at Arcor, and the server > only supports TLS 1.0. Still, Icedove can connect to that server just > fine. Also, "security.tls.version.min" is set to 0 by default > (indicating SSLv3 as the least supported version). So, there definitely > is some kind of fallback. > > Maybe that's the fallback that TLS provides anyway. A TLS 1.2-capable > client connecting to a server will say something like "I support TLS > 1.0-1.2, please use the best you can". A properly configured server will > then choose the latest supported version. This fallback is > cryptographically protected against downgrade attacks. And Icedove seems > to do it, else I would be unable to connect to Arcor's IMAP server.
propably you are right. I haven't yet any problems depending on this bug report. But I'm also no professional for anything related to mail server and there configuration. Unfortunately the exim maintainers haven't say something about this topic, so yes, maybe the conclusion in the NEWS and DEBIAN.readme are not fully correct. But as longer I think about it I'm willing to say you are right and mostly the server configs are not fully correct, especially for the settings around the Ciphersuites. Also unfortunately Mozilla hasn't a really clear changelog there we can see that's really changed inside the release. The full changelog [1] for version 31 nor the Thunderbird Blog [2] made a clear statement. > Firefox/Iceweasel has an *additional* layer of fallback in case the > first attempt fails, which can be caused by incorrect TLS > implementations on the server or a middlebox. *That* fallback is > currently not protected against downgrade attacks, it's the one that > enables Poodle, and it could be mitigated by TLS_FALLBACK_SCSV [1]. > Maybe that's the fallback that Icedove/Thunderbird do not do? In this > case, the NEWS is phrased fairly misleading, I think. It should clarify > that servers with older TLS versions will generally work just fine, but > a very small fraction of servers that have broken TLS implementations, > or than run behind firewalls breaking TLS, could cease to function. > > [1] <https://tools.ietf.org/html/draft-ietf-tls-downgrade-scsv-00> Thanks for your advices, I think we have to readjust some things in one of the next Debian version with a new NEWS files. I will talk to Christoph and Guido how to solve this. [1] https://www.mozilla.org/en-US/thunderbird/31.0/releasenotes/buglist.html [2] https://blog.mozilla.org/thunderbird/ Regards Carsten -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
