Disallowing ssl2

Mel fbsd.questions at rachie.is-a-geek.net
Tue Nov 11 06:37:10 PST 2008

On Tuesday 11 November 2008 14:50:56 John Almberg wrote:
> My server got an audit for PCI compliance and was red-flagged for
> allowing SSL2 connections, which they have some problem with. They
> want the server to use SSL3 or TLS:
> "Synopsis : The remote service encrypts traffic using a protocol with
> known weaknesses. Description : The remote service accepts
> connections encrypted using SSL 2.0, which reportedly suffers from
> several cryptographic flaws and has been deprecated for several
> years. An attacker may be able to exploit these issues to conduct man-
> in-the-middle attacks or decrypt communications between the affected
> service and clients. See also : http://www.schneier.com/paper-ssl.pdf
> Solution: Consult the application's documentation to disable SSL 2.0
> and use SSL 3.0 or TLS 1.0 instead. See http://support.microsoft.com/
> kb/216482 for instructions on IIS. See http://httpd.apache.org/docs/
> 2.0/mod/mod _ssl.html for Apache. Risk Factor: Medium  / CVSS Base
> Score : 2 (AV:R/AC:L/Au:NR/C:P/A:N/I:N/B:N) "
> They want me to do this for https, imaps, and pop3s protocols...
> Before I dig into this, I was wondering, is this even possible? Will
> anything break as a result?

Only corner cases. SSLv2 was quite short-lived. I can't remember client 
implementations that had SSLv2 without TLS/v3, so I looked it up:

"The SSL protocol was originally developed by Netscape. Version 1.0 was never 
publicly released; version 2.0 was released in 1994 but "contained a number 
of security flaws which ultimately led to the design of SSL version 3.0", 
which was released in 1996 (Rescorla 2001)."

So it would break ancient clients, think superspeed 56kB dial-up internet 

Problem with today's modular software: they start with the modules
    and never get to the software part.

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