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Old 02-18-2002, 09:29 PM   #1
Registered: Apr 2001
Location: MA
Distribution: redhat 7.2
Posts: 182

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My first hack

System redhat 7.1

I telnet'd to my system to find a login prompt of
"/usr/tux/backup/login: Bad Address"
I couldn't login as root or anyone else for that matter even though my web server, samba and ftp was working fine.

I found some links on google on how to fix it and surprisingly was up and running in about an hour. I can login and everything seems fine but I don't know how to confirm that. Could there be a trojan on the system?

I have a dsl router that can block services (I don't know which ones I should block). It also does port forwarding and I was forwarding telnet and ftp to my server. I've stopped that for now but http is open for my web server. I'd like to bring telnet and ftp back on line but i'm nervous.

What can ipchains or firewalls do to stop hacks if they come in thru telent or ftp? Is there a security problem with telnet or wu-ftp? (I thought I saw a reference to this on google)

Any help appreciated.
Old 02-19-2002, 02:57 PM   #2
Registered: May 2001
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(Why are you expecting a trojan? Any susceptible behaviour?) Since ure using RH there are some options. Unfortunately they involve things like installing integrity detection like Tripwire (rpm is on the cd) or Aide, and saving the rpm (and tripwire) databases on read-only media.

On to checking, the first step should be to consult what and have to say on this (unless you know the drill they offer good checklists), like here.
Ok, knowing login and any other binary could be trojaned, and your kernel "patched" with some module :-] you can still *try* to verify installed apps against the rpm database but if a compromise has taken place it ain't to be considered trustworthy.
To try to detect std rootkit strings in trojaned binaries you could use chkrootkit, using rkscan or the like. *Using chkrootkit on a suspectedly h4x0red box requires clean binaries. Either boot an fd/cd with them on it or examine the partition from another one.

About telnetd you're right. It should be banned. Login, passwords and the rest of the traffic are sent unencrypted. Use OpenSsh instead.
Wu has a history of bad glitches, bugs snafu's and whatnot. Alternatives to try could be Pro-ftpd, vsftpd, muddleftpd and I'm sure the list of more secure ftp daemons is longer. My criteria would be among others: Don't allow anonymous access unless you totally need it. Use tcp wrappers if you can. Block traffic from IP ranges belonging to "non routable" traffic. Don't use a daemon that can't drop root privileges after starting up. Use a daemon that doesn't rely on external binaries but provides 'em itself. Use chroot for lowering possible damages where possible.

Netfilter (kernel 2.4 using Ipchains or Iptables) doesn't stop "hacks". For a short description of the differences and why you should deploy an fw *and* some form of IDS see

Old 02-19-2002, 03:54 PM   #3
Registered: Apr 2001
Location: MA
Distribution: redhat 7.2
Posts: 182

Original Poster
Rep: Reputation: 30
Thanks for the response.

After reading threads on google and elsewhere my problem is systomatic of a rootkit trojan. I have reinstalled a couple of modified binaries to regain access but by nature, I may loose access again if it's a trojan.

I'm going to download a rootkit checker and take it from there.



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