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                     chkrootkit V. 0.54

      Nelson Murilo <nelson@pangeia.com.br> (main author)
        Klaus Steding-Jessen <jessen@cert.br> (co-author)

      This program locally checks for signs of a rootkit.
     chkrootkit is available at: http://www.chkrootkit.org/


             No illegal activities are encouraged!
     I'm not responsible for anything you may do with it.

       This tool includes software developed by the
       DFN-CERT, Univ. of Hamburg (chklastlog and chkwtmp),
       and small portions of ifconfig developed by
       Fred N. van Kempen, <waltje@uwalt.nl.mugnet.org>.
  1. What's chkrootkit?

chkrootkit is a tool to locally check for signs of a rootkit. It contains:

  • chkrootkit: a shell script that checks system binaries for rootkit modification.

  • ifpromisc.c: checks if the network interface is in promiscuous mode.

  • chklastlog.c: checks for lastlog deletions.

  • chkwtmp.c: checks for wtmp deletions.

  • check_wtmpx.c: checks for wtmpx deletions. (Solaris only)

  • chkproc.c: checks for signs of LKM trojans.

  • chkdirs.c: checks for signs of LKM trojans.

  • strings.c: quick and dirty strings replacement.

  • chkutmp.c: checks for utmp deletions.

chkwtmp and chklastlog try to check for deleted entries in the wtmp and lastlog files, but it is not guaranteed that any modification will be detected.

Aliens tries to find sniffer logs and rootkit config files. It looks for some default file locations -- so it is also not guaranteed it will succeed in all cases.

chkproc checks if /proc entries are hidden from ps and the readdir system call. This could be the indication of a LKM trojan. You can also run this command with the -v option (verbose).

  1. Rootkits, Worms and LKMs detected

For an updated list of rootkits, worms and LKMs detected by chkrootkit please visit: http://www.chkrootkit.org/

  1. Supported Systems

chkrootkit has been tested on: Linux 2.0.x, 2.2.x, 2.4.x and 2.6.x, FreeBSD 2.2.x, 3.x, 4.x and 5.x, OpenBSD 2.x, 3.x and 4.x., NetBSD 1.6.x, Solaris 2.5.1, 2.6, 8.0 and 9.0, HP-UX 11, Tru64, BSDI and Mac OS X.

  1. Package Contents

README README.chklastlog README.chkwtmp COPYRIGHT chkrootkit.lsm

Makefile chklastlog.c chkproc.c chkdirs.c chkwtmp.c check_wtmpx.c ifpromisc.c strings.c chkutmp.c

chkrootkit

  1. Installation

To compile the C programs type:

make sense

After that it is ready to use and you can simply type:

./chkrootkit

  1. Usage

chkrootkit must run as root. The simplest way is:

./chkrootkit

This will perform all tests. You can also specify only the tests you want, as shown below:

Usage: ./chkrootkit [options] [testname ...] Options: -h show this help and exit -V show version information and exit -l show available tests -d debug -q quiet mode -x expert mode -r dir use dir as the root directory -p dir1:dir2:dirN path for the external commands used by chkrootkit -n skip NFS mounted dirs

Where testname stands for one or more from the following list:

aliens asp bindshell lkm rexedcs sniffer w55808 wted scalper slapper z2 chkutmp amd basename biff chfn chsh cron crontab date du dirname echo egrep env find fingerd gpm grep hdparm su ifconfig inetd inetdconf identd init killall ldsopreload login ls lsof mail mingetty netstat named passwd pidof pop2 pop3 ps pstree rpcinfo rlogind rshd slogin sendmail sshd syslogd tar tcpd tcpdump top telnetd timed traceroute vdir w write

For example, the following command checks for trojaned ps and ls binaries and also checks if the network interface is in promiscuous mode.

./chkrootkit ps ls sniffer

The -q' option can be used to put chkrootkit in quiet mode -- in this mode only output messages with infected' status are shown.

With the `-x' option the user can examine suspicious strings in the binary programs that may indicate a trojan -- all the analysis is left to the user.

Lots of data can be seen with:

./chkrootkit -x | more

Pathnames inside system commands:

./chkrootkit -x | egrep '^/'

chkrootkit uses the following commands to make its tests: awk, cut, egrep, find, head, id, ls, netstat, ps, strings, sed, uname. It is possible, with the `-p' option, to supply an alternate path to chkrootkit so it won't use the system's (possibly) compromised binaries to make its tests.

To use, for example, binaries in /cdrom/bin:

./chkrootkit -p /cdrom/bin

It is possible to add more paths with a `:'

./chkrootkit -p /cdrom/bin:/floppy/mybin

Sometimes is a good idea to mount the disk from a compromised machine on a machine you trust. Just mount the disk and specify a new rootdir with the `-r' option.

For example, suppose the disk you want to check is mounted under /mnt, then:

./chkrootkit -r /mnt

  1. Output Messages

The following messages are printed by chkrootkit (except with the -x and -q command options) during its tests:

"INFECTED": the test has identified a command probably modified by a known rootkit;

"not infected": the test didn't find any known rootkit signature.

"not tested": the test was not performed -- this could happen in the following situations: a) the test is OS specific; b) the test depends on an external program that is not available; c) some specific command line options are given. (e.g. -r ).

"not found": the command to be tested is not available;

"Vulnerable but disabled": the command is infected but not in use. (not running or commented in inetd.conf)

  1. A trojaned command has been found. What should I do now?

Your biggest problem is that your machine has been compromised and this bad guy has root privileges.

Maybe you can solve the problem by just replacing the trojaned command -- the best way is to reinstall the machine from a safe media and to follow your vendor's security recommendations.

  1. Reports and questions

Please send comments, questions and bug reports to nelson@pangeia.com.br and jessen@cert.br.

A simple FAQ and Related information about rootkits and security can be found at chkrootkit's homepage, http://www.chkrootkit.org.

  1. ACKNOWLEDGMENTS

See the ACKNOWLEDGMENTS file.