Operating System:

Published:

06 March 2000

Protect yourself against future threats.

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              AUSCERT External Security Bulletin Redistribution
                             
                      ESB-2000.037 -- FreeBSD-SA-00:03
                  Asmon/Ascpu ports fail to drop privileges
                                07 March 2000

===========================================================================

FreeBSD have released the following security advisory concerning a
vulnerability in the asmon/ascpu packages provided as part of the FreeBSD
ports collection.  This vulnerability may allow local users to gain
root privileges.

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FreeBSD-SA-00:03                                           Security Advisory
                                                                FreeBSD, Inc.

Topic:          Asmon/Ascpu ports fail to drop privileges

Category:       ports
Module:         asmon/ascpu
Announced:      2000-02-19
Affects:        Ports collection before the correction date.
Corrected:      2000-01-29
FreeBSD only:   yes

I.   Background

Two optional third-party ports distributed with FreeBSD can be used to
execute commands with elevated privileges, specifically setgid kmem
privileges. This may lead to a local root compromise.

II.  Problem Description

Asmon and ascpu allow users to execute arbitrary commands as part of a user
configuration file. Both applications are Linux-centric as distributed by
the vendor and require patching to run under FreeBSD (specifically, using
the kvm interface and setgid kmem privileges to obtain system statistics);
this patching was the source of the present security problem. This is a
similar flaw to one found in the wmmon port, which was corrected on
1999/12/31.

Note that neither utility is installed by default, nor are they "part of
FreeBSD" as such: they are part of the FreeBSD ports collection, which
contains over 3100 third-party applications in a ready-to-install format.

FreeBSD makes no claim about the security of these third-party
applications, although an effort is underway to provide a security audit of
the most security-critical ports.

III. Impact

If you have not chosen to install the asmon or ascpu ports/packages, then
your system is not vulnerable. If you have, then local users can obtain
setgid kmem rights, which allows them to manipulate kernel memory, and
thereby compromise root.

IV.  Workaround

Remove the asmon and ascpu ports/packages, if you have installed them.

V.   Solution

One of the following:

1) Upgrade your entire ports collection and rebuild the asmon and/or ascpu
ports.

2) Reinstall a new package obtained from:

ftp://ftp.freebsd.org/pub/FreeBSD/ports/packages/sysutils/asmon-0.60.tgz
ftp://ftp.freebsd.org/pub/FreeBSD/ports/packages/sysutils/ascpu-1.8.tgz

after the correction date. At the time of advisory release, the asmon
package was not available - you may need to use one of the other methods
to update the software.

3) download a new port skeleton for the asmon and/or ascpu ports from:

http://www.freebsd.org/ports/

and use it to rebuild one or both ports.

4) Use the portcheckout utility to automate option (3) above. The
portcheckout port is available in /usr/ports/devel/portcheckout or the
package can be obtained from:

ftp://ftp.freebsd.org/pub/FreeBSD/ports/packages/devel/portcheckout-2.0.tgz

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