Malware Uses Linux Systems as Proxies

A Trojan horse (defined) is compromising Linux systems by exploiting poorly implemented SSH (Secure Shell)(defined) remote access. Many are already compromised systems first have a new account created with a notification to the Trojans authors providing the details of the system enabling a remote connection. The Trojan then installs the Satanic Socks Server utility to set up proxy server (defined) for use by the attackers or any individual they chose to connect to your system (very likely for a fee). More information on this threat is available here and here.

How Can I Protect Myself from This Threat?

If you are an administrator of Linux servers/workstations you should ensure remote SSH access uses a strong authentication mechanism. If this access is not required, strongly consider disabling SSH access.

To check if your Linux system has already been compromised, you can list the user accounts from a Linux system using the commands below. If you locate any suspicious accounts, you can delete them. I will also provide other useful commands below:

cat /etc/passwd
: this will list the name of user accounts
grep :0: /etc/passwd : will find accounts with the string “”:0″” within them (accounts with root privileges)

crontab -l -u root : display cron jobs (defined) scheduled by root and any other UID 0 accounts

Attackers often schedule jobs that include backdoors on the machine guaranteeing the attacker return access to the system.

The above commands are particularly useful if you already know the outputs of these commands when your system is working fine/as expected. You can then compare those known good outputs to the current output to more easily determine if your system has been compromised.

If you find a rogue/unknown user account; you can delete it using the following command:

userdel -r [account name]

where [account name] is the name of the user account that you wish to delete.

I hope that the above information is useful to you in protecting your Linux systems against this threat.

Thank you.

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