Dec 132010
 

The home page for LMD is located at:
Linux Malware Detect | R-fx Networks

cpanel.net info on maldet

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

What is Linux Malware Detect (LMD)?

Linux Malware Detect (LMD) is a malware scanner for Linux released under the GNU GPLv2 (free, open source) license, that is designed around the threats faced in shared hosted environments. It uses threat data from network edge intrusion detection systems to extract malware that is actively being used in attacks and generates signatures for detection. In addition, threat data is also derived from user submissions with the LMD checkout feature, threats found on the TCH network of over 30,000 hosted domains and from malware community resources.

The result, is a malware scanner with over 2,200 signatures and growing, that detects a varied assortment of malware from the infamous Yellsoft Darkmailer CGI Mailer to the more common r57 PHP Command Shell to BASE64 Encoded file injection strings.

Installation & Configuration:

There is nothing special to installing LMD, download the package and run the enclosed install.sh script:

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]

tar xfz maldetect-current.tar.gz
cd maldetect-*
./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
</rohan></ryan></proj>

Now that LMD is installed, take note of the file locations and we can go ahead with opening the configuration file located at /usr/local/maldetect/conf.maldet for editing (vi or nano -w). 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 anyways.

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 interchangeable with the short form flags (i.e: –scan-recent vs. -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.

Report Location

The malware detect scan reports are stored in /usr/local/maldetect/sess with file names similar to session.hits.082311-0402.8042
or they can be accessed via the following;
maldet -e, or –report SCANID
View scan report of the most recent scan or provided SCANID
e.g: maldet –report (shows last scan)
e.g: maldet –report 050910-1534.21135 (shows specific date scan)

Release & Signature Updates
Updates to the release version of LMD are not automatically installed but can be installed using the –update-ver option. There is good reasons that this is not done automatically and I really dont feel like listing them so just think about it a bit.

The latest changes in the release version can always be viewed at: http://www.rfxn.com/appdocs/CHANGELOG.maldetect

The LMD signatures are updated typically once per day or more frequently depending on incoming threat data from the LMD checkout feature, IDS malware extraction and other sources. The updating of signatures in LMD installations is performed daily through the default cron.daily script with the –update option, which can be run manually at any time.

An RSS & XML data source is available for tracking malware threat updates:
RSS: R-fx Networks – Linux Malware Detect Updates
XML: http://www.rfxn.com/api/lmd?id=recent
XML: http://www.rfxn.com/api/lmd?id=all

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:
Upgrade CentOS 4.8 to 5.3 | R-fx Networks

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.

Ignore Files:
There are three ignore files available and they break down as follows:

/usr/local/maldetect/ignore_paths
A line spaced file for paths that are to be execluded from search results

/usr/local/maldetect/ignore_sigs
A line spaced file for signatures that should be removed from file scanning

/usr/local/maldetect/ignore_inotify
A line spaced file for paths that are to be excluded from inotify monitoring

NOTE: These scans are thorough and can take days if your home dir is large, you have 8 million files or 1200 domains on the server…. just saying. This tool is more suited for specific accounts or directories that may be compromised. So, if you run this and do a full homedir scan and t takes 8 days, don’t blame me, you have been warned :D

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