Date: Sun, 22 Feb 2004 19:48:52 -0800 From: Tim Kientzle <tim@kientzle.com> To: David Schultz <das@FreeBSD.ORG> Cc: kientzle@acm.org Subject: Re: cvs commit: src/sbin/nologin Makefile nologin.c Message-ID: <40397824.3080607@kientzle.com> In-Reply-To: <20040223025647.GA43467@VARK.homeunix.com> References: <200402221003.i1MA3PW0024791@repoman.freebsd.org> <403944D8.6050107@kientzle.com> <20040223025647.GA43467@VARK.homeunix.com>
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David Schultz wrote:
> On Sun, Feb 22, 2004, Tim Kientzle wrote:
>>Colin Percival wrote:
>>
>>> Report login attempts to syslog. Due to the statically-linked nature of
>>> nologin(8) ...
>>
>>Why is nologin statically linked?
>
> Because of environment-poisoning attacks such as the following:
>
> das@VARK:~> setenv LD_LIBRARY_PATH /home/das/exploit
> das@VARK:~> \login -p test
>
> This attack was executed with a dynamically-linked /sbin/nologin
> and a special libc.so.5 in the /home/das/exploit directory that
> replaces the _exit() stub with a routine that spawns a shell.
Hmmmm.... Several other solutions come immediately to mind:
* Handle this in pam (or even in login)
(Just check if the user's shell is /sbin/nologin and
reject the login if it is.)
* Install /sbin/nologin setuid nobody or setgid nogroup
That would disable LD_LIBRARY_PATH processing for it.
* Have login -p not pass LD_LIBRARY_PATH
Of these, the first is arguably the best, the second easiest
to implement. The third I'm unsure about; I can't
really picture a scenario where login -p should pass
LD_LIBRARY_PATH, but that's hardly conclusive.
I agree, by the way, that there should be a way to
"mark" a program as ignoring LD_LIBRARY_PATH at
compile-time (other than making it setuid/setgid).
Tim Kientzle
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