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Date: Wed, 04 Feb 2015 17:55:34 +0100
From: Florent Daigniere <florent.daigniere@...stmatta.com>
To: oss-security@...ts.openwall.com
Subject: Re: Apache 2.4 mod_ssl SSLSessionTickets -- others
vulnerable?
On Wed, 2015-02-04 at 10:35 -0600, Mark Felder wrote:
> From the 2.4.12 changelog:
>
>
> *) mod_ssl: New directive SSLSessionTickets (On|Off).
> The directive controls the use of TLS session tickets (RFC 5077),
> default value is "On" (unchanged behavior).
> Session ticket creation uses a random key created during web
> server startup and recreated during restarts. No other key
> recreation mechanism is available currently. Therefore using
> session
> tickets without restarting the web server with an appropriate
> frequency
> (e.g. daily) compromises perfect forward secrecy. [Rainer Jung]
>
>
> So if you use Apache 2.4 and care about PFS protecting your data, you
> should turn this feature off. This appears to be an implementation issue
> because there is no other way for Apache to recreate keys. I don't know
> a lot about the fine details of Session Tickets, but can anyone care to
> comment if there are other known bad implementations of session tickets
> out there? Does this affect Apache 2.2? Nginx? Lighttpd?
>
>
> Thanks
> I find this bizarre that a known security weakness like this is left
> "on" by default...
You're right, it's "bizarre"
I've tried to make some noise about it two years ago [1] ...
IMHO it's OpenSSL's default that should be changed. The server
implementation shouldn't give a ticket if it's picked a PFS enabled
cipher (or a cipher which aims at providing better security than
AES128-CBC) unless explicitly told to do so (the case where there is
more than one server).
Apache HTTPd's new setting (SSLSessionTicketKeyFile), allowing you to
set the ticket key is *DANGEROUS* as documented [1]. It encourages users
explicitly to store the key on a forensically carvable medium...
"The ticket key file contains sensitive keying material and should be
protected with file permissions similar to those used for
SSLCertificateKeyFile."
Which is exactly what you shouldn't do!
Regards,
Florent
[1]
https://media.blackhat.com/us-13/US-13-Daigniere-TLS-Secrets-Slides.pdf
[2]
https://httpd.apache.org/docs/2.4/mod/mod_ssl.html#sslsessionticketkeyfile
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