Find malicious scripts on Linux — Linux Malware detect

wget http://www.rfxn.com/downloads/maldetect-current.tar.gz

tar xfz maldetect-current.tar.gz
cd maldetect-*
./install.sh

To scan servers with CPanel: maldet -b -a /home/?/public_html/?
To check current scan status: tail -f /usr/local/maldetect/event_log
To check reports: maldet –report list
To open a particular report: maldet –report <REPORT–ID>

Download & More info

The home page for LMD is located at:
http://www.rfxn.com/projects/linux-malware-detect

The current version of LMD is always available at the following URL:
http://www.rfxn.com/downloads/maldetect-current.tar.gz
http://www.rfxn.com/appdocs/README.maldetect
http://www.rfxn.com/appdocs/CHANGELOG.maldetect

Related reading:
http://www.rfxn.com/linux-malware-detect-v1-3-3-making-good-things-better/
http://www.rfxn.com/signature-updates-rss-feed/
http://www.rfxn.com/better-late-than-never-linux-malware-detect-1-3/

Installation & Configuration

Installing LMD is a very easy process, lets get right into it:

root@praxis [~]# wget http://www.rfxn.com/downloads/maldetect-current.tar.gz
2010-05-15 23:34:05 (148 MB/s) - `maldetect-current.tar.gz' saved [268031/268031]

root@praxis [~]# tar xfz maldetect-current.tar.gz
root@praxis [~]# cd maldetect-*
root@praxis [~]# ./install.sh
Linux Malware Detect v1.3.4
            (C) 1999-2010, R-fx Networks <proj@r-fx.org>
            (C) 2010, Ryan MacDonald <ryan@r-fx.org>
inotifywait (C) 2007, Rohan McGovern <rohan@mcgovern.id.au>
This program may be freely redistributed under the terms of the GNU GPL

installation completed to /usr/local/maldetect
config file: /usr/local/maldetect/conf.maldet
exec file: /usr/local/maldetect/maldet
exec link: /usr/local/sbin/maldet
cron.daily: /etc/cron.daily/maldet

maldet(32517): {sigup} performing signature update check...
maldet(32517): {sigup} local signature set is version 2010051510029
maldet(32517): {sigup} latest signature set already installed

Now that LMD is installed, take note of the file locations as that is the next thing we need to do. Lets go ahead and open the configuration file located at /usr/local/maldetect/conf.maldet:

root@praxis [~]# nano -w /usr/local/maldetect/conf.maldet

The configuration file is fully commented so you should be able to make out most options but lets take a moment to review the more important ones:

email_alert
This is a top level toggle for the e-mail alert system, this must be turned on if you want to receive alerts.

email_addr
This is a comma spaced list of e-mail addresses that should receive alerts.

quar_hits
This tells LMD that it should move malware content into the quarantine path and strip it of all permissions. Files are fully restorable to original path, owner and permission using the –restore FILE option.

quar_clean
This tells LMD that it should try to clean malware that it has cleaner rules for, at the moment base64_decode and gzinflate file injection strings can be cleaned. Files that are cleaned are automatically restored to original path, owner and permission.

quar_susp
Using this option allows LMD to suspend a user account that malware is found residing under. On CPanel systems this will pass the user to /scripts/suspendacct and add a comment with the maldet report command to the report that caused the users suspension (e.g: maldet –report SCANID). On non-cpanel systems, the users shell will be set to /bin/false.

quar_susp_minuid
This is the minimum user id that will be evaluated for suspension, the default should be fine on most systems.

The rest of the options in conf.maldet can be left as defaults unless you clearly understand what they do and how they may influence scan results and performance.

Usage & Manual Scans

The usage of LMD is very simple and there is a detailed –help output that provides common usage examples, I strongly recommend you check the –help output and spend a few minutes reviewing it.

The first thing most users are looking to do when they get LMD installed is to scan a certain path or series of paths. An important note is that LMD uses the ‘?’ character for wildcards instead of the ‘*’ char. In the below examples I will be using the long form flags but they are interchangable with the short form flags (i.e: –scan-recent = -r).

If we wanted to scan all user public_html paths under /home*/ this can be done with:

maldet –scan-all /home?/?/public_html

If you wanted to scan the same path but scope it to content that has been created/modified in the last 5 days you would run:

maldet –scan-recent /home?/?/public_html 5
If you performed a scan but forget to turn on the quarantine option, you could quarantine all malware results from a previous scan with:

maldet –quarantine SCANID

Similarly to the above, if you wanted to attempt a clean on all malware results from a previous scan that did not have the feature enabled, you would do so with:

maldet –clean SCANID

If you had a file that was quarantined from a false positive or that you simply want to restore (i.e: you manually cleaned it), you can use the following:

maldet –restore config.php.2384
maldet –restore /usr/local/maldetect/quarantine/config.php.2384

Once again, I encourage you to fully review the –help output for details on all options and the README file for more details on how LMD operates.

Daily Scans

The cronjob installed by LMD is located at /etc/cron.daily/maldet and is used to perform a daily update of signatures, keep the session, temp and quarantine data to no more than 14d old and run a daily scan of recent file system changes.

The daily scan supports Ensim virtual roots or standard Linux /home*/user paths, such as Cpanel. The default is to just scan the web roots daily, which breaks down as /home*/*/public_html or on Ensim /home/virtual/*/fst/var/www/html and /home/virtual/*/fst/home/*/public_html.

If you are running monitor mode, the daily scans will be skipped and instead a daily report will be issued for all monitoring events. If you need to scan additional paths, you should review the cronjob and edit it accordingly.

To check current status of the running scan:

$ tail -f /usr/local/maldet/event_log

To check available reports:

$ maldet –report list

This will return a list of scan reports available.

$ maldet –report <SCANID>

Real-Time Monitoring

The inotify monitoring feature is designed to monitor users in real-time for file creation/modify/move operations. This option requires a kernel that supports inotify_watch (CONFIG_INOTIFY) which is found in kernels 2.6.13+ and CentOS/RHEL 5 by default. If you are running CentOS 4 you should consider an inbox upgrade with:
http://www.rfxn.com/upgrade-centos-4-8-to-5-3/

There are three modes that the monitor can be executed with and they relate to what will be monitored, they are USERS|PATHS|FILES.

      e.g: maldet --monitor users
      e.g: maldet --monitor /root/monitor_paths
      e.g: maldet --monitor /home/mike,/home/ashton

The options break down as follows:
USERS – The users option will take the homedirs of all system users that are above inotify_minuid and monitor them. If inotify_webdir is set then the users webdir, if it exists, will only be monitored.
PATHS – A comma spaced list of paths to monitor
FILE – A line spaced file list of paths to monitor

Once you start maldet in monitor mode, it will preprocess the paths based on the option specified followed by starting the inotify process. The starting of the inotify process can be a time consuming task as it needs to setup a monitor hook for every file under the monitored paths. Although the startup process can impact the load temporarily, once the process has started it maintains all of its resources inside kernel memory and has a very small userspace footprint in memory or cpu usage.

The scanner component of the monitor watches for notifications from the inotify process and batches items to be scanned, by default, every 30 seconds. If you need tighter control of the scanning timer, you can edit inotify_stime in conf.maldet.

The alerting of file hits under monitor mode is handled through a daily report instead of sending an email on every hit. The cron.daily job installed by LMD will call an –alert-daily flag and send an alert for the last days hits. There is also an –alert-weekly option that can be used, simply edit the cron at /etc/cron.daily/maldet and change the –alert-daily to –alert-weekly.

Terminating the inotify monitoring is done by passing the ‘-k|–kill-monitor’ option to maldet, it will touch a file handle monitored by maldet and on the next waking cycle of the monitor service, it will terminate itself and all inotify processes

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