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Date: Thu, 16 Apr 2009 13:36:58 +0200
From: Tomas Hoger <>
Cc:, "Wietse Venema" <>
Subject: Re: Re: Some fun with tcp_wrappers

Hi Steve!

On Wed, 15 Apr 2009 20:44:49 -0400 (EDT) "Steven M. Christey"
<> wrote:

> I'm not sure how to handle this from a CVE perspective

I'm not too surprised...  This is not too usual case, that's why I
tried to initiate this discussion here and make others aware.

>  - if the API functions perform as documented, as Wietse says, then
>    separate CVEs would need to be assigned for applications that
>    misuse the API.
>  - If there is a separate bug that causes tcp_wrappers to
>    allow hosts in ways that are contrary to specification, then that
>    would be treated as a problem in tcp_wrappers (whether it's from
>    Wietse or some downstream modification).

Wietse already confirmed current behavior is the expected one, which is
what I mentioned before in both bug and the first mail in this thread.
It can be argued whether it's also documented one, as man more reads to
me as STRING_UNKNOWN is some special value, rather than a regular
hostname "unknown".

Wietse, I'm not trying to blame you for this or anything, I'm only
facing a problem that needs to be resolved.  The fact that the proposed
change is already included in tcp_wrappers packages in Fedora for some
time (so the "break compatibility" harm was done already) is part of
the problem.  Making sure all relevant applications are changed
upstream to not use hosts_ctl and later reverting the change is one of
the possible resolutions.

The good_client (tcp_wrappers wrapping function in portmap /
nfs-utils / ...) problem is rather interesting too, as it creates
problems due to its attempt to avoid unneeded DNS lookups (workaround
for hosts_ctl limitation?) and support host aliases (tcp_wrappers
limitation).  Any idea why hostname alias support was coded on the
application level, rather than on the tcp_wrappers level?  Those using
good_client may argue, that using thinner wrapper over tcp_wrappers may
break existing setups relying on hostname aliases and, again, blame
tcp_wrappers for not doing what "it should".

Steve, giving CVEs to applications wouldn't be much easier either, and
is likely to result in some finger-pointing anyway (this only causes
problem with hostname-bases rules, such rules should be more strongly
discouraged in the documentation anyway, due to reliance on properly
working DNS).  No easy or obvious right way to word it at the moment,
it seems.  Apps using good_client are likely to need separate CVE(s)

Tomas Hoger / Red Hat Security Response Team

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