Cracked Linux Boxes Used to Wield Windows Botnets

m-stone writes "Online auction house eBay recently did a threat assessment to better understand the forces ranging against them. The company is keeping the fine details under wraps, but the biggest source of danger for the company is apparently botnets. You're never going to guess who was running them. '[Dave Cullinane, eBay's chief information and security officer] noticed an unusual trend when taking down phishing sites. 'The vast majority of the threats we saw were rootkitted Linux boxes, which was rather startling. We expected Microsoft boxes,' he said. Rootkit software covers the tracks of the attackers and can be extremely difficult to detect. According to Cullinane, none of the Linux operators whose machines had been compromised were even aware they'd been infected. Because Linux is highly reliable and a great platform for running server software, Linux machines are desired by phishers, who set up fake websites, hoping to lure victims into disclosing their passwords."

Comments

Confirmed

[mccalli]

I've noticed a large increase in attempts to crack my co-lo Linux servers recently, and it must be said that two got through (shared site, some customers running old content management apps and the kits hit). When we watched the behaviour of the cracked box, it was connecting back to...I think undernet.org or similar?...and sending controls via IRC. Plus doing a spot of spamming of its own bat.

Our set-up is that we have a host OS install doing nothing but running VMware Server and then any real stuff gets done in a VM, so this was easy for us to recover from quickly via VM snapshotting. But still, it's a trend that's noticeably on the increase.

Cheers,
Ian

Re:Confirmed

[mccalli]

Fortunately, each user has their own account, so i can easily check which user owns any malicious processes or files that appear on the system.

May want to be careful about that assumption. A lot of these things go out under the apache user and the mails via the www-data@somehost.invalid account.

Look for tell-tale things like apache processes running when you're an apache2-only site (they're disguised processes that are really something else, obviously). Do an ls -al in all the home directories, look for directories whose name is just a space character, check /tmp isn't mounted executable...that kind of thing.

Cheers,
Ian

Windows vs. Linux

[derian_cf]

I work for a fairly well known dedicated server provider. If I had to give a rough estimate, I'd say we're 40% Windows and 60% Linux environments. Not surprisingly, the number of boxes that get hacked (rooted entirely or not) is about equal between the two, however the purpose for which they're hacked is generally quite different. 80% of the hacked Linux boxes are used for UDP floods, things like that. Also IRC bots. Interestingly enough, in my 6 months working there, I don't believe I've ever seen a Windows box used for phishing. They're always used for FTP servers hosting movies/music/programs and/or IRC servers doing the same thing.

Brute Force Attacks

[superbrose]

I'm sure pretty much everybody who is running a Linux server (or any server as a matter of fact), especially with services like SSH enabled, is currently subject to brute force attacks.

When I looked at my auth log I noticed a huge amount of brute force attacks for all my servers, so I installed denyhosts, which seems to work fine.

I guess the problem is also that in many distributions SSH servers are configured to allow root logins, and if nobody looks at the log files these go totally unnoticed.

Re:Brute Force Attacks

[Russell Coker]

Run your sshd on a port other than 22. Most attackers only scan the well-known ports. Running your sshd on a different port removes a lot of the noise from your logs and allows you to concentrate on the real issues.

The "Host" sections in the /etc/ssh/ssh_config file allows you to specify which port to use for each host you connect to (so you don't need to type "-p 1234" every time you connect).

Re:Good News & Bad News

[morgan_greywolf]

Yes. You should Here's what I do. (I guess you could say these are some security tips for those running Linux boxes at home and leaving them up on the Net):

• Run a hardware NAT firewall/router. Any ol' Linksys, Dlink or Netgear thang will do. Just remember it's not the be all and end all to security problems.
• Open as few ports as absolutely possible. I have nothing open on my router except port 22 and BitTorrent, and I don't leave BitTorrent running all the time
• Check your logs at least once a day. Look for any suspicious signs -- missing log entries, ssh connects you weren't expecting, services running that you don't normally have running, NICs going into promiscuous mode unexpectedly, excessive mail being pumped through any MTAs, etc.
• When running OpenSSH, I disallow password authentication. This prevents problems with users due to the use of stupid passwords. My sshd only accepts a valid RSA key exchange as acceptable authorization.
• Regularly update and run rootkit checkers. These are not be all end all, but they help spot obvious rootkits
• Make cron jobs that regularly scan your system for unusual permissions -- world writeable, binaries that are setuid, etc. and for suspicious files. There are programs and scripts that will do this for you. STFW or check with your distro.
• Perform MD5 checking on your files and executables, espcially.
• Regularly check your /etc/passwd and /etc/group files for new or unusual entries.
• Don't run NIS -- it's inherently insecure. You should be using OpenLDAP if you need directory authorization on your network.