Linux Detecting / Checking Rootkits with Chkrootkit and rkhunter Software

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Q. Most rootkits use the power of the kernel to hide themselves, they are only visible from within the kernel. How do I detect rootkits under CentOS or Debian Linux server?

A.. A rootkit is a program (or combination of several programs) designed to take fundamental control (in Unix terms “root” access, in Windows terms “Administrator” access) of a computer system, without authorization by the system’s owners and legitimate managers.

Detecting rootkits under Linux

You can try the following tools to detect Linux rootkits:

WARNING! These examples should run from Live CD (Linux Live Security CD) for the best result.

Zeppoo Software

Zeppoo – Zeppoo allows you to detect rootkits on i386 and x86_64 architecture under Linux, by using /dev/kmem and /dev/mem. Moreover it can also detect hidden tasks, connections, corrupted symbols, system calls and so many other things. Download source code here

Chkrootkit Software

Chkrootkit – chkrootkit is a tool to locally check for signs of a rootkit. Type the following command to install chkrootkit
$ sudo apt-get install chkrootkit
Start looking for rootkits, enter:
$ sudo chkrootkit
Look for suspicious strings, enter:
$ sudo chkrootkit -x | less
You need to specify the path for the external commands used by chkrootkit such as awk, grep and others. Mount /mnt/safe using nfs in read-only mode and set /mnt/safe binaries PATH as trusted one, enter:
$ sudo chkrootkit -p /mnt/safe

rkhunter software

rkhunter – rkhunter (Rootkit Hunter) is a Unix-based tool that scans for rootkits, backdoors and possible local exploits. rkhunter is a shell script which carries out various checks on the local system to try and detect known rootkits and malware. It also performs checks to see if commands have been modified, if the system startup files have been modified, and various checks on the network interfaces, including checks for listening applications. Type the following command to install rkhunter:
$ sudo apt-get install rkhunter
The following command option tells rkhunter to perform various checks on the local system:
$ sudo rkhunter --check
The following command option causes rkhunter to check if there is a later version of any of its text data files:
$ sudo rkhunter --update
The following option tells rkhunter which directories to look in to find the various commands it requires:
$ sudo rkhunter --check --bindir /mnt/safe

Recommended readings:

  • man pages – rkhunter and chkrootkit
  • rkhunter Project home page
  • chkrootkit Project home page

Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin and a trainer for the Linux operating system/Unix shell scripting. He has worked with global clients and in various industries, including IT, education, defense and space research, and the nonprofit sector. Follow him on Twitter, Facebook, Google+.

8 comment

  1. A more sophisticated and effective solution for Linux rootkit detection is Second Look. It is a Linux memory forensics product that uses kernel and process integrity verification to detect stealthy kernel- and user-mode malware. It supports all distros running 2.6- and 3-series kernels on 32- or 64-bit x86 systems. A large, continuously updated repository of reference kernels and hashes of vendor-distributed software support the fully automatic verification process. Learn more about it at http://secondlookforensics.com/.

  2. A more sophisticated and effective solution for Linux rootkit detection is Second Look. It is a Linux memory forensics product that uses kernel and process integrity verification to detect stealthy kernel- and user-mode malware. It supports all distros running 2.6- and 3-series kernels on 32- or 64-bit x86 systems. A large, continuously updated repository of reference kernels and hashes of vendor-distributed software support the fully automatic verification process. (Full disclosure: I am one of the developers of Second Look.)

  3. what is the reason to install the tool (sudo apt-get… ) on a system you already suspect infected ? Would be interesting to have instructions how to update/run it from a DVD or other nonwritable media

  4. After downloading the files from chkrootkit.org, there is source code for chkdirs.c, chkproc.c, etc., but not for chkrootkit. Only the executable for chkrootkit is downloaded. How can we trust this? How do we know that chkrootkit is not infecting our Macs with key loggers?

  5. Who has reviewed the source code for all of the chkrootkit C programs, especially the script “chkrootkit”, to ensure that they aren’t doing infecting our computers with rootkits or key loggers?

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