[CentOS] SELinux threads, cynicism, one-upmanship, etc.
lowen at pari.edu
Sat Nov 19 03:29:09 UTC 2005
On Friday 18 November 2005 21:59, Les Mikesell wrote:
> On Fri, 2005-11-18 at 20:30, Lamar Owen wrote:
> > What is the most critical injury on academic networks today? Think about
> > it a while, as it's not what you think; but rooting a box has a lot to do
> > with it, and it's on the inside network typically.
> Unless its different than every other network, it's windows boxes
> loaded with spyware and spam-sending zombies.
Yes, this is correct. What are the lessons a Linux admin can learn from the
Windows malware scourges, some of which don't require you to be running as an
If anything, the spyware/zombie scourge should be the driving force behind
SELinux adoption to prevent the same thing from happening to the Linux boxes
(a well-place root hole and a linux-aware Windows spyware/worm, and your
Linux box is owned from the inside). Is it too far of a leap to want to nip
the coming scourge in the bud? Linux boxes are not immune as long as root
holes exist that can leverage root's superuser powers, unfettered by role
based and mandatory access controls. If there is no superuser in the
traditional sense, the root hole is useless. Completely useless.
Firewalls are of no use, either. All it takes is a root hole in a program
that is visible to the inside network with all the spyware laden Windows
boxes (samba or cups, perhaps); rootkit the apache httpd installation with a
fragrouting daemon which uses IP over HTTP tunneling (or a rootkitted bind
and IP over DNS tunneling) and you are owned, ready to become another zombie,
but this time from your server. With the typical wide-open outbound firewall
rules, you're even ready to become a DDoS zombie.
You might think I'm paranoid; the black hats are indeed this devious and are
indeed using devices like this today. If SELinux can help plug a few cracks,
then it's worth learning and using.
I have had the experience of having a box get a rootkit; it is not a pleasant
experience, and taught me a valuable lesson. Yes, the box had a firewall in
front of it. No, it didn't help. While it was back in 1998, it is a lesson
I will never forget.
The investigators who contacted me afterwards told me that this particular
incident involved over 20,000 hosts, all compromised in the space of 14
hours. Scripted, using a BIND root hole. Hit my public DNS server; used
carefully crafted packets on TCP port 53 for remote root shell. Happened
before the patch was available for BIND. Happened before chrooted BIND was
commonly available. The first file they transferred out was /etc/shadow.
The only common advice used today that would have thwarted that exploit was
running BIND chrooted. It was a necessary service, and only necessary
services were running. Patches were up to date; it was exploited prior to
the vulnerability being publicly disclosed. Firewall was in place; hit on
and used port 53 for all communication. Did not require a reboot. Rootkit
installed replaced many (but not all) system utilities and covered tracks in
the system logs. SELinux would have thwarted the vulnerability as surely as
I found the rootkit by simple visual inspection about 25 minutes after the
hack; I had just come to work, and had hit the SHIFT key to deactivate the
console screen saver. On that virtual console, I always left an instance of
'top' running; the display was customized to show the data I was interested
in. I caught the rootkit because the rootkit version of top didn't honor my
I was alerted by CERT of the hack two weeks later. They had traced the ftp
transfer of the rootkit from a known compromised server to mine. I replied
that I had already contained the problem, and had rebuilt the server from
distribution media, and had upgraded the version of BIND. This was when I
found out the extent of the attack.
I have had the 'rare' exploit used against my servers; everything that helps
security without being too cumbersome is a big win in my book.
Director of Information Technology
Pisgah Astronomical Research Institute
1 PARI Drive
Rosman, NC 28772
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