Document version: 20111021 19:04:14 UTC A current copy of this document may be found on the ERACC web site here: http://www.eracc.com/content/your-system-has-been-cracked-not-hacked Document author: Gene Alexander of ERA Computers & Consulting Contact ERACC about this document: support at eracc dot com Your Linux, UNIX, or other computer system has been cracked (not hacked, see bottom). 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. 4. BACKUP ANY DATA YOU NEED TO KEEP. 4a. (By Pep 2001-12-21) 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. (By Andreas Braeutigam 2002-02-26) (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 / drive. 6a. (By Bill Unruh 2001-12-21) Then, scan all of the files which you saved for suid programs: find / -perm +6000 -ls 6b. (By Bill Unruh 2001-12-21) 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. 6b1. (By Moe Trin 2005-10-06) That works with rpm assuming no one has "gotten to" the rpm database. Note that quite a few distributions are rpm based and can use this test. For a Debian based system, use 'debsums -s'. 6c. (By Pep 2001-12-21) 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. (By Bill Staehle 2002-01-07) 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 or behind a firewall with all services on the PC OFF 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. (By Andreas Braeutigam 2002-02-26) 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. (By Pep 2001-12-21) 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. (By Pep 2001-12-21) 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. (By Bill Staehle 2002-01-01) [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. (By James Knott 2002-01-02) 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. (By Pep 2001-12-21) 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. (By Bill Staehle 2002-01-01) [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: http://www.linuxsecurity.com/docs/colsfaq.html 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://aplawrence.com/consultants.html https://www.redhat.com/apps/reseller_catalog/ http://www.commandprompt.com/community/consultants/guide Certified or Authorized resellers and/or consultants should be able to assist you. A certification or authorization is not a true indicator of ability as so many pointy-haired-bosses seem to believe (http://www.dilbert.com/). With or without a certification 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.catb.org/~esr/jargon/html/C/cracker.html http://www.catb.org/~esr/jargon/html/H/hacker.html Most of all Good Luck! ---------------------------------------------------------------------- Need a web host? http://www.powweb.com/join/index.bml?AffID=558115&LinkName=text-docs