Re: Hacked? How?

From: Bit Twister (BitTwister@localhost.localdomain)
Date: 01/27/03


From: Bit Twister <BitTwister@localhost.localdomain>
Date: Mon, 27 Jan 2003 11:48:39 GMT

On Sun, 26 Jan 2003 19:36:23 -0700, scaryogre wrote:
> Hi,
>
> I was sitting near my RH 7.3 server last night and saw quite a bit of
> activity flashing on the hub which is unusual since it is just a family
> website. On a lark, I decided to do a tcpdump to see what was going on.
> To my horror I saw an established connection with
> lemming.euronet.nl.ircd. A netstat -a showed two established ircd
> connections.
>
> I know that somehow my system was compromised, but I do not understand
> to what extent just yet. I ran chkrootkit and it found nothing (only a
> few suspicious files that I reviewed and did not seem problematic).
>
> Any ideas? I believe the standard process is to always assume the
> intruder got root. Do I need to format and reinstall?

Here is why you need a FORMAT and clean install when your box IS cracked.
   http://en.tldp.org/LDP/LG/issue36/kuethe.html
4'th paragraph.

Think about that paragraph.
You cannot use ANY of your pc's utilities to see if your box is cracked
and find what addtional files are installed.

What you can do is have a dual boot system. You install a second copy of
your OS and label it Auditor. You never, EVER mount it from the internet OS.

Some have suggested install on a seperate disk which is left unplugged until
you want to use it.

Anytime you THINK you've been cracked, you can boot into Auditor, mount the
internet os partition and start checking the internet OS partitions for new
files and whatnot.

Any time you KNOW your're box is cracked, you should:
o Pull the box off the network. You do not want the police taking
        you and your equipment to jail because a cracker used it
        to crack a bank or military site. If the cracker removes their
        backtracks to their box, you get to do the jail time.

o Put the hardrive(s) into a standalone machine,
        mount the disk(s) readonly,
        save any data, user files, ...,

o Save a full copy of the disk(s) for your forensic attempt,
        save the disk(s) for FBI forensics if it's a Big, BIG dollar loss.

o Re-FORMAT disk drives and do a fresh install from known clean
        source to remove any possible back doors and/or password sniffers
        the cracker installed.

o Restore your saved files, verify that the restored files
        do not have the suid bit set "find / -perm +6000 -ls".

o Have everyone on the box's network change passwords and
        tell them that the cracker may have been running a
        password sniffer so they will not use the passwords ever again.
        Any other boxes logged into from the cracked box should
        have their passwords changed.

Install a modern firewall. Example: iptables is better than ipchains.
If you have a spare linux computer, you can use it to port scan
your box with nmap from http://www.insecure.org/nmap/

Get all the vendor updates to your distro.

You might want to read Armoring Linux
http://www.ibiblio.org/pub/Linux/docs/HOWTO/other-formats/html_single/Security-Quickstart-HOWTO.html
http://www.linuxdoc.org/HOWTO/Security-Quickstart-HOWTO/index.html
http://www.enteract.com/~lspitz/linux.html
http://www.ibiblio.org/pub/Linux/docs/HOWTO/Security-Quickstart-Redhat-HOWTO
http://www.ibiblio.org/pub/Linux/docs/linux-doc-project/solrhe/Secur
ing-Optimizing-Linux-RH-Edition-v1.3.txt

        http://www.linuxsecurity.com/docs/colsfaq.html
        http://www.securityportal.com/lskb/articles/
        http://www.securityportal.com/lasg/
keep an eye on
        http://www.cert.org/advisories/

Never login as root unless you have to.
Set the mailer deamon to send root's email to your user account.
Do not surf the net as root. Root's browser should have everthing
disabled, javascript, java, cookies, style sheets, auto anything.
Always login from the console, no su, telnet, ssh,..
That way a keystroke logger in your user account cannot
catch your root login password.

You can audit your system if you are using the rpm package manager with
  rpm -Va | grep '..5' > /tmp/verify.log
Runs for a while; more than 5 minutes.

/tmp/verify.log will contain changes which you have made using
configuration tools

Hope crackers do not put in a rootkit which makes the rpm check obsolete.
I think this has happened, though not sure. On one of my boxes
it cored after about 2 minutes, log looked like it ran but never completes
the audit.

rpm -Va | grep '^..5' will give you a warm feeling about what changed.
That warm feeling might turn into the warm feeling you get when
you do not get to the bathroom in time. :(

The cracker could install trojaned files some where else and modify
PATH to use them instead of the files you just checked.
You could look at the report and see
        S.5....T c /root/.bash_profile
        S.5....T c /root/.bashrc
You see that and say, "Ok, I did change those. No problem."
BZZZZzzit. WRONG answer, Cracker changed your PATH and you are
running his code.

It also does not show additional files. I have created a site file in
/etc/profile.d which puts my site/bin into PATH.

Cracker can add his own cracked.sh file to change/add to PATH and
create aliases to substitute a stock command for his code.



Relevant Pages

  • Re: Ip Address
    ... The system was already taken over, why the user login was still ... Here is why you need a FORMAT and clean install when your box IS cracked. ... That will tell you about known root kits if you have one. ... The cracker may not have installed a rootkit. ...
    (comp.os.linux.security)
  • Re: unintended wireless?
    ... Here is why you need a FORMAT and clean install when your box IS cracked. ... That will tell you about known root kits if you have one. ... The cracker may not have installed a rootkit. ... Always login from the console, no su, telnet, ssh,.. ...
    (alt.computer.security)
  • Re: Ive been hacked...tips for a postmortem?
    ... Here is why you need a FORMAT and clean install when your box IS cracked. ... That will tell you about known root kits if you have one. ... The cracker may not have installed a rootkit. ... EVER mount it from the internet OS. ...
    (comp.os.linux.security)
  • Re: unintended wireless?
    ... >Here is why you need a FORMAT and clean install when your box IS cracked. ... That will tell you about known root kits if you have one. ... >The cracker may not have installed a rootkit. ... >Always login from the console, no su, telnet, ssh,.. ...
    (alt.computer.security)
  • Re: what files does rh-sharpe and ambiant install ??
    ... > This probably was due to one of the rootkits. ... Here is why you need a FORMAT and clean install when your box IS cracked. ... Never login as root unless you have to. ... The cracker could install trojaned files some where else and modify ...
    (comp.os.linux.security)