Date: Sun, 14 Jul 2002 01:57:34 -0700 From: "Crist J. Clark" <crist.clark@attbi.com> To: freebsd-security@FreeBSD.ORG Subject: Re: FreeBSD Security Advisory FreeBSD-SA-02:29.tcpdump Message-ID: <20020714085734.GD56656@blossom.cjclark.org> In-Reply-To: <200207131731.g6DHVRs92032@lurza.secnetix.de> References: <200207122046.g6CKk2tG099856@freefall.freebsd.org> <200207131731.g6DHVRs92032@lurza.secnetix.de>
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On Sat, Jul 13, 2002 at 07:31:27PM +0200, Oliver Fromme wrote:
> FreeBSD Security Advisories <security-advisories@freebsd.org> wrote:
> > [...]
> > IV. Workaround
> >
> > There is no workaround, other than not using tcpdump.
>
> Well, you can at least set up the system in a way so you
> don't have to run tcpdump as root: Create a special group,
> chgrp /dev/bpf* to that group and make them group-readable
> (writable is not required). Then add all users to that
> group which should be allowed to use tcpdump.
tcpdump(8) can still be exploited to run abitrary code as that user.
> An even better approach would be to create a pseudo user
> (similar to the nobody user) which is a member of the
> tcpdump group, and write a small wrapper script which
> uses /usr/bin/su to call tcpdump as that pseudo-user.
>
> Of course, that's only a quick workaround, not a solution.
It's not really a workaround, it just mitigates the potential for
damage should the bug be exploited.
> On a related matter: It would probably be a very good idea
> for tcpdump to drop priviledges right after opening the BPF
> device.
tcpdump(8) never has elevated privileges. It just runs as whoever
executes it. As you say, the way to run it at lower privileges is to
give a less privileged user read access to the bpf(4) devices.
--
Crist J. Clark | cjclark@alum.mit.edu
| cjclark@jhu.edu
http://people.freebsd.org/~cjc/ | cjc@freebsd.org
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