I've Just Been Hacked, Now What?

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I've Just Been Hacked, Now What?

Postby kostyanj » Tue Mar 25, 2003 6:47 pm

Check your machine with http://www.chkrootkit.org/ IF it doesn't show up anything this doesn't mean you are clean, if you suspect it follow the below:

Afterwards, to secure your machine, read:


Courtesy of a newsgroup post:

Gene <gene-at-eracc.hypermart.net>

Your Linux, UNIX, etc. box has been cracked. What now?

1. Disconnect the infected system NOW! Don't wait.

2. Get *all* patches for your OS version a.s.a.p. (Now! Today!)

3. Save the patches to another system / drive / CDR / etc.


4a. (Suggested by Pep <PepMozilla-at-netscape.net> 12-21-2001)
Do not include any binary programs in your backup as these
may have been compromised. You should re-install binary
programs and libraries from their original medium.

5. Wipe the OS partition / drive clean.
(You are unlikely to be able to clean up a compromised system by
hand. So, grit your teeth and reformat that sucker.)

5a. (Suggested by Andreas Braeutigam <abrae-at-freenet.de> 02-26-02)
(This is *not* an exact quote but is a paraphrase)
Reformat may give the wrong impression that a time consuming
format of the entire drive is needed. Rather than reformat
the entire drive wipe out the MBR, partition boot sectors
root partition and any other partition containing executable
files that may be compromised.

6. Reinstall the OS + apps and restore data to the clean partition /

6a. (Suggested by Bill Unruh <unruh-at-physics.ubc.ca> 12-21-2001)
Then, scan all of the files which you saved for suid

find / -perm +6000 -ls

6b. (Suggested by Bill Unruh <unruh-at-physics.ubc.ca> 12-21-2001)
Make sure that each of those files which are reported
should actually be suid or sgid.
If they are system files, check them with:

rpm -Vf /name/of/file

If they are in your or others home directories, they almost
certainly should not be suid, especially not suid root.
For example a file in /tmp, or in /usr/share/man should
never be suid root.

6c. (Suggested by Pep <PepMozilla-at-netscape.net> 12-21-2001)
When you restore your backup, check all system configuration
files that are restored for any cracks that may have already
been incorporated into these files.

6d. (Suggested by Bill Staehle <withheld on req.> 01-07-2002)

find / \( -nouser -o -nogroup \) -exec ls -lad {} \;

and if anything turns up, determine _why_ the user and/or
group is not in /etc/passwd and/or /etc/group. Who _really_
owns those files/directories? What are they?

7. WHILE OFFLINE install all the patches.

8. Create your own, unique hidden directory and 'cp' files to it
that are essential to system maintenance like 'ls', 'netstat',
'route', 'ifconfig', 'ps', etc.
(Should you be cracked again, God forbid, as long as you don't
have a compromised kernel this will allow you to use these copies
to "see" what a cracker may have done.)

8a. (Suggested by Andreas Braeutigam <abrae-at-freenet.de> 02-26-02)
I'd rather store those copies on a separate system or a
non-writeable medium. [like a CD-R, floppy diskette with
write protect on, etc.]

8b. (Suggested by Pep <PepMozilla-at-netscape.net> 12-21-2001)
Check your final installation to see that all known security
bugs have been addressed. There are various utilities that
you can get to help with this, such as port scanners; etc.

8c. (Suggested by Pep <PepMozilla-at-netscape.net> 12-21-2001)
Install some of the security monitors that exist out there.
I can't give you the names of all of these but there are
monitors like portsentry that constantly scan for connections
to your system, also there are other utilities that
constantly check your system logs and ones that constantly
check the system configuration files for any modifications of
content and/or permissions.

8d. (Suggested by Bill Staehle <withheld on req.> 01-01-2002)
[It] would be better if the program files you put into that
hidden directory are statically compiled, and not using the
possibly corrupted dynamic libraries. It also assumes that
the kernel doesn't get messed with. _At this time_ these
concerns are not big, but why not stay ahead?

8e. (Suggested by James Knott <james.knott-at-rogers.com> 01-02-02)
Mount as much of your filesystem as possible as read only. If
the crackers can't write to a partition, they can't change
it. Rename and hide su etc. [as suggested in 8].

9. Then, and only then, set the box up to get online.

10. (Suggested by Pep <PepMozilla-at-netscape.net> 12-21-2001)
Finally, design and implement a regular backup procedure,
something you should already have done, so that you can limit
any future problems you might have with your system, whether from
cracking; bad configuration; system failure or simply bad users.

10a. (Suggested by Bill Staehle <withheld on req.> 01-01-2002)
[For further security] you could have another system sitting
off a separate network, that randomly grabs a file off of
this box, and does a file comparison externally. If that
other system is not accepting ANY connections from ANYWHERE,
it makes a better intrusion detection system.

What if you have only one machine with one OS installed? You still
need to disconnect, backup and reinstall. To get the patches ask a
friend or acquaintance with a secured system to help download the
patches. Or see if your OS vendor offers the current patches on CD.
If so, order it.

For further reference see the comp.os.linux.security FAQ:

Finally, if all this is too much for you to handle alone consider
hiring an expert to assist you or to do it for you. However, be aware
hiring a consultant that is able to help will probably *not* be
inexpensive. For Linux and UNIX consultants in your area check These:

http://www.redhat.com/products/purchase ... eller.html

("-" Suggested by Bill Staehle <withheld on req.> 01-07-2002)
-Those are anonymous FTP servers. Log in as anonymous, with your
-email address as password, and change to the indicated directory.
-Look for the file "MIRRORS" to find a list of other servers that
-may be more accessabhle to you. Then continue down from this
-directory to ./docs/linux-doc-project/linux-consultants-guide/
-and get one of the versions of the Consultants-Guide:

Certified or Authorized resellers and/or consultants will be the
ones most likely to be able to assist you. Those well versed in
Linux and/or UNIX are usually capable of handling the "lesser OS's"
as well.

Finally, NEVER use the word "hacking" to describe "cracking" as there
is a significant difference between a "cracker" and a "hacker". See:

http://www.tuxedo.org/~esr/jargon/html/ ... acker.html
http://www.tuxedo.org/~esr/jargon/html/ ... acker.html

Most of all Good Luck!
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